From what I've read, Canada is going EPA cert only motors. Local shops are shutting down because they can't import motors anymore. I'd triple check with the vendor you pick that it is possible. Or pick one up from a Canadian vendor, some places still have them in stock(cheaper shipping too). So be careful ordering from the US.
More info on engines in Canada
As for your chopper bike, You'll definately need an offset motor mount(or build one). Because of the fat back tire, you'll need to have your sprocket stick out farther too. Like extra washers or something.
Offset Motor Mount(ebay)
Brakes... You'd be pushing your luck with the stock rear drum if you had to make an emergency stop... eep. You might want to look into a front disc hub, or someway to mount some V-brakes.
Oh, and check out the Google search at the top, all results link back here.