A little surprising, as I didn't even consider a CFL player would win. Cornish was the obvious choice for Most Outstanding Player in the CFL, which is a rarity for a non-import. Cornish probably benefits from no other obvious athlete having a fantastic year (Milos Ranoic has had a good year for a Canadian tennis player, but certainly wasn't close to a slam or anything). 2013 isn't an Olympic year either which probably helps (soccer player Christine Sinclair won it last year).
In case you are wondering, the last CFL winner was McMaster alumnus Russ Jackson in 1969, that rarity in the CFL a starting Canadian quarterback.