A.M. Best Co. has assigned a rating of a+ to the existing C$300 million subordinated debentures of Sun Life Assurance Co. of Canada.

The firm has also assigned an a+ rating to the US$300 million subordinated notes issued by Sun Canada Financial Co. and the US$600 million cumulative capital trust securities issued by Sun Life of Canada (U.S.) Capital Trust I.

The U.S. dollar-denominated securities are unconditionally guaranteed by Sun Life. The A++ (Superior) financial strength rating of Sun Life and its principal life/health subsidiaries is unaffected.

A.M Best says the ratings reflect Sun Life’s leading market position in Canada and the United States, diversified earnings sources, strong operating performance, sophisticated asset-liability management practices and superior capitalization.