Unfortunately, one of those areas than would take a constitutional amendment to get uniform laws across the country.

In Canada, rifles and shotguns show up at auctions, but the auctioneer must demand an approved license with police check before handing the gun over. Handguns that show up in estates (unless licensed target types) must be turned over to the police, and it is not easy to re-register the target guns.
Rifles and shotguns must be registered (national registry) but there is much opposition, at least in western Canada, and some hunters refuse to register.

The drug gangs here in Canada all have handguns, brought across the border with little difficulty.