The mutated wolverines would really svck. We would also have mutated mountain lions to worry about.
On the other hand, the Mountains have plenty of nice trails, and would make semi decent cover.
Depends where in the prairies. Manitoba's hydro-electric capacity would be a target, as would Canada's largest bio lab located in Winnipeg. Saskatchewan's oil capacity could also be a target. That's not even mentioning the massive beating North Dakota would take in an attempt to take out American capacity, and the fallout that would come north because of it. The prairies would not be as safe as you might think.
Plus mutated beavers, those little [censored]s are angry enough as it is!
(I'm originally from the Canadian prairies)