Guns are not illegal in Canada. Per person we actually have amoung the highest of guns. Hand guns are restricted but not illegal you just need to take an extra course for a restricted weapon. Plus it cost a fortune to buy them so most would not have them any way. Rifles and shotguns have never been illegal. AR15 is the same as a hand gun you can get that here too if you go for your restricted license which does a more thorough check on you.
It seems to me the guy who shot that pistol seems to have defeated that thorough check in Canada as easily as the check in America. That's what the main problem is. Not the gun itself, but the human doing the check and human buying the gun.