TORONTO (Reuters) - Sun Life Financial (>> Sun Life Financial Inc.), Canada's No. 3 life insurer, said on Wednesday it fell to a third-quarter net loss due to charges related to the sale of its U.S. annuities business, but operating profit topped estimates.

Toronto-based Sun Life took a C$844 million loss on the annuities business, which it sold during the quarter as part of a push to reduce its exposure to uncertain stock markets and interest rates.

On a net basis, Sun Life lost C$520 million ($499.30 million), or 84 Canadian cents a share, in the quarter, compared with a year-before profit of C$383 million, or 64 Canadian cents per share.

Excluding the impact of the sale, operating income was C$422 million, or 69 Canadian cents a share, down from a year-earlier C$459 million, or 77 Canadian cents a share.

The results beat analysts' expectations of a profit of 64 Canadian cents a share, according to Thomson Reuters I/B/E/S.

Sun Life has spent the last several quarters working to reduce its market exposure through hedging and re-aligning its business.

Operating income was reduced by C$111 million due in part to assumption changes related to insurance contract liabilities, compared to a year-earlier gain of C$164 million.

Premiums and deposits on a continuing operations basis rose to C$32.9 billion from C$26.1 billion.

Earlier on Wednesday, Industrial Alliance Insurance and Financial Services (>> Industrial Alliance Insur. & Fin. Ser.), Canada's No. 4 insurer, reported a stronger-than-expected profit of C$105.8 million, or C$1.07 a share, up from a year-before profit of C$103.3 million, or C$1.09 a share.

($1 = 1.0415 Canadian dollars)

(Reporting by Cameron French; Editing by Bob Burgdorfer and Leslie Gevirtz)