They do exchange data as many a fleeing criminal on either side of the border have been caught and apprehended there, both Canadian and American fugitives both. And the Canadian border patrol service dosen't fuck around with criminals coming from the land of the NRA and almost certainly packing heat. They are armed and armoured with modern gear and the training to use it. Same as airport cops in YVR (Vancouver International Airport) who patrol both inside and outside the secure area with assault rifles open carried point down.
As well, America does not recognize Canadian pardons, so a check on the Canadian side would show nothing for a Canadian citizen, on the U.S. side that conviction for shoplifting or selling weed when you were 19 will show up just fine, and as like as not bar you from entry.
