Vermont has the most liberal gun laws in the US, and has the lowest crime rate. El Paso, Texas' murder rate is half of Vancouver's and one fifth of Thunder Bay's. There is no evidence that gun laws will make a difference one way or the other. Besides, gun laws won't affect 2/3s of your murders, because they are not with guns.
The US has and strict laws on machine guns since 1934, about the same as your handgun registry. Canadian machine gun restrictions were laxer until 1977. I have never read about machine gun crimes up there.
The last time I looked, ammunition was going for as much as $10 or $12 per round.
On the black market? Or Canadian gun stores?
We can't keep drugs from coming from Mexico. How many Canadian crime guns originate in the US? Is there RCMP trace data to verify this?
Gun control groups in the US like to claim that most of the crime guns found in New York and DC come from Virginia, but the ATF trace data does not show that.