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ANNUAL REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

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TRANSITION REPORT PURSUANT TO SECTION 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934

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REPORT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

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FINANCIAL STATEMENTS AS OF AND FOR THE YEARS ENDED DECEMBER 31, 2003      AND 2002:

     Statements of Net Assets Available for Benefits

4

     Statements of Changes in Net Assets Available for Benefits

5

     Notes to Financial Statements

6-9

SUPPLEMENTAL SCHEDULE AS OF DECEMBER 31, 2003*:

     Form 5500, Schedule H, Part IV, Line 4i - Schedule of Assets (Held at End of Year)

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SIGNATURES

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INDEX TO EXHIBIT

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SUN LIFE ASSURANCE COMPANY OF CANADA (U.S.)

UNITED STATES EMPLOYEES' SUN ADVANTAGE

SAVINGS AND INVESTMENT PLAN

STATEMENTS OF NET ASSETS AVAILABLE FOR BENEFITS

DECEMBER 31, 2003 AND 2002

2003

2002

ASSETS:

   Investments, at fair value:

      Mutual Funds

$   96,967,142

$   68,466,043

      Vanguard Retirement Savings Trust

39,244,817

37,229,655

      Sun Life Financial Stock Fund

2,532,600

1,265,707

      Participant Loans

2,720,549

2,843,747

      Cash

1,748,362

      1,507,009

              Total investments

143,213,470

111,312,161

Contributions receivable

       58,918

              52,927

NET ASSETS AVAILABLE FOR BENEFITS

$ 143,272,388 

$   111,365,088

See notes to financial statements.

SUN LIFE ASSURANCE COMPANY OF CANADA (U.S.)

UNITED STATES EMPLOYEES' SUN ADVANTAGE

SAVINGS AND INVESTMENT PLAN

STATEMENTS OF CHANGES IN NET ASSETS AVAILABLE FOR BENEFITS

YEARS ENDED DECEMBER 31, 2003 AND 2002

2003

2002

ADDITIONS:

  Investment activity:

    Net appreciation (depreciation)

$ 17,274,377

$     (17,262,344)

    Interest

1,790,703

1,853,128 

    Dividends

           1,381,425

           1,286,812 

            Total investment activity

       20,446,505

       (14,122,404)

  Contributions:

    Employer

4,492,859

4,044,135 

    Participants

12,639,723

11,967,830 

    Employee rollovers

           863,040

           1,216,885 

            Total contributions

        17,995,622

         17,228,850 

            Total additions

        38,442,127

           3,106,446 

DEDUCTIONS:

  Benefits paid to participants

6,534,827

6,062,376 

  Distribution to insurance carrier for provision of benefits

                0

                51,788 

            Total deductions

           6,534,827

           6,114,164 

NET INCREASE (DECREASE)

31,907,300

(3,007,718)

NET ASSETS AVAILABLE FOR BENEFITS:

  Beginning of year

        111,365,088

        114,372,806 

  End of year

$     143,272,388

$      111,365,088 

See notes to financial statements.

1.

DESCRIPTION OF THE PLAN

The following brief description of the Sun Life Assurance Company of Canada (U.S.) United States Employees' Sun Advantage Savings and Investment Plan (the "Plan") is provided for general information purposes only. Participants should refer to the Plan document for more complete information.

General - The Plan was originally established on April 1, 1986 by Sun Life Assurance Company of Canada (the "Corporation") for the benefit of its employees and the employees of its subsidiaries that elected to become participating employers under the Plan. The purpose of the Plan is to permit eligible employees of the Corporation and participating employers to defer and receive employer-matching contributions in order to provide funds for employees in the event of death, disability, unemployment and retirement. Any employee, 21 years or older, shall be eligible to become a participant in the Plan as soon as administratively feasible after his first day of employment. The Plan is subject to the provisions of the Employee Retirement Income Security Act of 1974 ("ERISA").

Effective January 1, 2002, the Corporation transferred sponsorship of the United States Employees' Sun Advantage Savings and Investment Plan to its wholly owned subsidiary Sun Life Assurance Company of Canada (U.S.) (the "Company" or "Plan Sponsor").

Contributions - Once an employee becomes eligible to participate in the Plan, he or she may elect to become a participant by entering into a salary reduction agreement. The agreement provides that the participant agrees to accept a reduction in compensation in an amount equal to 1% to 60% of his or her compensation for 2003 and 2002. During 2002, the Plan adopted Age 50 Catch Up Contributions as a result of the Economic Growth and Tax Relief Reconciliation Act of 2001. All contributions made pursuant to the salary reduction agreement on behalf of the participant are deposited in the pooled participant accounts. Participant and Company contributions are invested, as directed by each participant, in one or more of the investment options offered by the Plan. Participant selections of one or more of the investment options must be in multiples of 1%.

The Company will make a matching contribution for each participant at the rate of $.50 for each $1.00 contributed by the participant to a pooled matching account, provided, however, that no matching contribution will be made for participant contributions in excess of 6% of compensation.

Participant Accounts - Individual accounts are maintained for each plan participant. Each participant's account is credited with the participant's contribution, the Company's matching contribution, and allocations of Plan earnings, and charged with an allocation of plan losses and investment related expenses.

Allocations are based on participant earnings or account balances, as defined. The benefit to which a participant is entitled is the benefit that can be provided from the participant's vested account.

Investments - Participants direct the investment of their contributions into various investment options offered by the Plan. Company contributions are invested in accordance with participant investment allocations. The Plan currently offers twelve mutual funds, Sun Life Financial Stock Fund, and a Stable Value Fund as investment options for participants.

Vesting - A participant is fully vested in the value of his or her share of the pooled participant accounts at all times. A participant becomes fully vested in the value of his or her share of the pooled matching accounts in accordance with the following schedule:

Years of Service

Vested Percentage

Greater than 1,000 hours

20%

2 years

40

3 years

60

4 years

80

5 years

100

A participant is fully vested in his or her share of the pooled matching accounts upon retirement at normal retirement age or older, disability, or death, regardless of the length of service.

Participant Loans - A participant may borrow up to 50% of his or her vested account balance with a maximum loan balance of $50,000. Repayment is effected through payroll deductions over a period of one to five years for non-mortgage loans and over a period of one to 15 years for mortgage loans. Loan repayments are credited against investments, as allocated in the participant's account. The participant is charged $50 for a loan application. Interest rates range from 4% to 11%. Maturity dates range to July 3, 2018.

Payment of Benefits - The Plan provides for normal retirement benefits to be paid to participants who have reached the age of 65. If the participant's service with the Company terminates, other than by reason of retirement, the participant may elect to receive his or her distribution following his or her termination of employment. Distributions will be made in installments or in a lump sum, except if the participant's account balance is $5,000 or less, in which case payment will only be made in a lump sum.

Forfeitures - In the event that a participant terminates service prior to completing five years with the Company, the nonvested portion or his or her share of the pooled matching accounts will be forfeited. At December 31, 2003 and 2002, forfeited nonvested accounts totaled $211,263 and $115,679, respectively. These accounts will be used to reduce the future company matching contributions. During the year ended December 31, 2003, employer contributions were reduced by $66,025.

2.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Accounting - The financial statements of the Plan are prepared in accordance with accounting principles generally accepted in the United States of America.

Use of Estimates - The preparation of financial statements in conformity with accounting principles generally accepted in the United States of America requires the plan administrator to make estimates and assumptions that affect the reported amounts of net assets available for benefits and changes therein. Actual results could differ from those estimates. The Plan utilizes various investment instruments, including mutual funds, collective trusts, and stocks. Investment securities in general, are exposed to various risks, such as interest rate, credit, and overall market volatility. Due to the level of risk associated with certain investments, it is reasonably possible that changes in the values of investments will occur in the near term and that such changes could materially affect the amounts reported in the financial statements.

Investment Valuation and Income Recognition - The Plan's investments are stated at fair value. Shares of mutual funds are valued at the net asset value of shares held by the Plan at year-end. Participant loans are stated at cost plus accrued interest, which approximates fair value.

Purchases and sales of securities are recorded on the trade-date basis. Interest income is recorded on the accrual basis. Dividends are recorded on the ex-dividend date.

Payment of Benefits - Benefit payments to participants are recorded upon distribution.

Administrative Expenses - Administrative expenses of the Plan are paid by the Plan sponsor.

Excess Contributions Payable - The Plan is required to return contributions received during the plan year in excess of the IRC limits.

PLAN ADMINISTRATOR AND TRUSTEE

The U.S. Benefit Plans Committee (the "Committee") is the named Plan Administrator and Trustee of the Plan. At December 31, 2003, the Committee consisted of six members: Janet V. Whitehouse, Claude Accum, Robert J. De Clercq, John T. Donnelly, Teresa A. Vellante Ham and Michael E. Shunney.

4.

FEDERAL INCOME TAX STATUS

The Plan obtained its latest determination letter dated October 29, 2002, in which the Internal Revenue Service stated that the Plan, as then designed, was in compliance with the applicable requirements of the Internal Revenue Code (the "Code"). The Plan has been amended since receiving the determination letter. However, the Committee believes that the Plan is currently designed and being operated in compliance with the applicable requirements of the Code. Therefore, no provision for income taxes has been included in the Plan's financial statements.

5.

PLAN TERMINATION

Although it is the intention of the Company to continue the Plan indefinitely, it is not under any obligation or liability to do so and may discontinue or terminate the Plan at its discretion. In the event of discontinuance of the Plan, all amounts that have been allocated to participants in both the pooled participant accounts and the pooled matching accounts will be distributed to them in accordance with the Plan Document.

6.

INVESTMENTS

The Plan's investments that represented 5% or more of the Plan's net assets available for benefits as of December 31 are as follows:

2003

2002

Mutual funds, at fair value:

  MFS Growth Opportunity Fund

$14,475,719

$ 10,693,995

  Massachusetts Investors Trust

12,805,686

9,994,622

  MFS Government Securities Fund

N/A

5,879,594

  MFS Total Return Fund

13,541,570

10,569,955

  Fidelity Blue Chip Growth Fund

19,230,652

13,634,069

  JP Morgan Capital Growth Fund

10,478,165

6,776,921

Collective trusts, at fair value -

   Vanguard Retirement Savings Trust

39,244,817

37,229,655

During 2003 and 2002, the Plan's investments in mutual funds (including gains and losses on investments bought and sold, as well as held, during the year) appreciated in value by $17,274,377 in 2003 and depreciated in value by $17,262,344 in 2002, respectively.

RELATED-PARTY TRANSACTIONS

Certain Plan investments are managed by the Corporation and its affiliates. The Plan's investments include common stock of Sun Life Financial Inc., an affiliate of the Plan sponsor. These transactions qualify as permitted party-in-interest transactions.

SUN LIFE ASSURANCE COMPANY OF CANADA (U.S.)

UNITED STATES EMPLOYEES' SUN ADVANTAGE

SAVINGS AND INVESTMENT PLAN

FORM 5500, SCHEDULE H, PART IV, LINE 4i - SCHEDULE OF ASSETS (HELD AT END OF YEAR)

DECEMBER 31, 2003

(a)

(b) Identity of Issue,

(c) Description of Investment,

(d) Current

      Borrower, Lessor

      Including Collateral, Rate

       Value

      or Similar Party

      of Interest, Maturity Date,

      Par or Maturity Value

Vanguard

  Retirement Savings Trust

$   39,244,817   

Mutual funds:

*

Massachusetts Financial Services

  MFS Growth Opportunity Fund - 

     1,802,704.684  shares

14,475,719

  MFS High Income Fund - 

     1,256,151.782 shares

4,974,361

  MFS Government Securities Fund - 

     553,677.240 shares

5,392,816

  MFS Total Return Fund - 

    896,792.652 shares

13,541,570

  Massachusetts Investors Trust - 

    819,826.275 shares

12,805,686

Fidelity Investments

  Fidelity Blue Chip Growth Fund - 

    485,254.902 shares 

19,230,652

  Fidelity Low-Priced Stock Fund - 

     95,566.742 shares 

3,342,925

Vanguard

Vanguard S & P 500 Index Fund -

    47,871.550 shares 

4,915,451

Vanguard Total Market Bond Index Fund -

     92,250.182 shares 

951,099

JP Morgan Fleming

  JP Morgan Capital Growth Fund -

    279,641.433 shares

10,478,165

T. Rowe Price

  International Stock Fund - 

    513,226.022 shares

5,896,967

  Equity Income Fund - 

    39,806.758 shares

             961,731

Total mutual funds

       96,967,142

*

Sun Life Financial

Sun Life Financial Inc. - Common Stock

     101,223.00 shares

         2,532,600

*

Plan participants

Loans to participants, secured by underlying

participant account balances, interest rates

From 4.00% to 11.00%, maturity

Dates through 2018

        2,720,549 

Cash

        1,748,362 

Contribution Receivable

             58,918 

TOTAL INVESTMENTS

$   143,272,388 

* Party-in-interest

Exhibit

Number

Description

    23

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM