Two points:
Trafficking of illegal guns, that are either purchased or stolen in Canada, is far less prevalent than trafficking in illegal guns from the US. If not for their lack of controls, we wouldn't have as many illegal guns on the street.
Because of our controls, it is more likely that someone who is purchasing guns and then selling them illegally will be caught.
As I have said, it would appear that our system works. If the US actually had a Federally based system I would say that it didn't work, but they don't have such a system.
The controls in Canada have no effect on illegal gun trafficking. You could buy as many as you wish & obliterate the serial numbers or circumvent the gun registration system entirely. Demand for illegal guns will create a market - it's that simple. If illegal guns didn't come from the US, more would come from other countries. Guns are no different than illegal drugs. People will continue to break laws & circumvent controls.
http://www.rcmp-grc.gc.ca/ci-rc/reports-rapports/traf/index-eng.htm