In the Canada section of this discussion forum, there was a thread about how likely it was for Canadians to meet someone who never visited the US.
It seemed like most people agreed that few Canadians have absolutely never visited the US at least once (especially considering how many Canadians live close to the border). It's mostly smaller town Canadians farther from the US border, or recent first-generation Canadians who haven't traveled to the US.
http://forum.skyscraperpage.com/showthread.php?t=231056
It's more common for Americans to have never crossed into either of the bordering countries on the north or the south, but I'm curious if they'd make up a majority or not?