Can't help you with firearms laws in Canada either. But the best AR-15 type rifles available are: Colt, Armalite, Bushmaster, and Rock River. The best value of the four is Rock River. DPMS makes servicable guns, but their bolt carrier assemblies are sometimes troublesome. They will usually make it right if you get a bad one, though.

The M-4 is a 14" barreled military carbine. Bushmaster puts a 2.5" muzzle brake on theirs to be legal for civilian sales. In the US, you would need a class 3 license to own a 14" barrel rifle.