CHICAGO--(BUSINESS WIRE)--Fitch Ratings expects to assign a rating of 'BBB+' to Sun Life Financial Inc.'s (SLF) C$500 million issuance of 2.60% subordinated unsecured debentures due 2025. KEY RATING DRIVERS This new issue is rated equivalent to the ratings of SLF's existing subordinated unsecured debt. The proceeds will be used to partially fund the acquisition of the employee benefits business of Assurant, Inc. and may also be used for general corporate purposes, which may include investments