300 + million....
I would also assume that their unprotected border and the war on drugs which has increased the amount of weapons on the black market by a lot also has a lot to do with gun violence in the US. We hear about incidents like this, but how many more that involve drug cartels are not covered?
Also, to address the point about, I do believe the AR-15 is allowed in Canada, but the 30 round clip is illegal IIRC. I've seen the AR-15 for sale at Wholesale Sports.