Okay, we're crossing streams here. You said 'Canada scrapped their registration plan' because it was costly and didn't work. That is only partially true. They scrapped the registration of 'non-restricted' guns - which are hunting rifles and shotguns - not 'all' guns as you seem to imply. Restricted guns, which include handguns, must still be registered and have always had to be registered. Prohibited guns are still prohibited. You must still pass a course and get a license to purchase *any* gun (level of license depends on type you want to buy). Quebec has re-enacted the 'non-restricted' gun registration, and *those* are the guns people are turning in as opposed to registering them. So, no one is turning in handguns, and other restricted guns, because they have *always* had to be registered. Tracking?
As to whether or not any of this prevents gun deaths/violence, that is debatable. What isn't debatable is how much lower Canada's gun deaths are per capita.