35 million Canadians, about the same population as California. Unfortunately MMA is an extremely niche sport up here, not 10% of Canadians have ever heard of GSP.
The news media spent more time on Sid Crosby's concussion (he didn't play for most of a year because of it) every day (pointless newcasts saying nothing had changed) than they spent on GSP even on days he fought. Hockey is really the only sport that counts here. Even women's curling gets (according to official network figures) 3-4 million viewers, which is 3-4 times as many viewers as GSP ever got.
It'd be nice if Canada supported MMA and GSP the way people on Sherdog think, but the reality is most people still have no idea about it. The only exception is young guys (ie guys under 25), and they tend not to have free money to pay for PPV's - and they tend to watch hockey by a long shot too. Of course, some say its because hockey has better fights.
Thinking GSP has a whole country behind him is like thinking say Anderson Silva had a whole country behind him. In Brazil its all about soccer (or football), in Canada its about hockey.
Why some people watch GSP is pretty simple, its the same reason some people watch Mayweather - people like to watch winners. Every sports team knows this. You don't have to be exciting as long as you're winning. If you start to lose you better be exciting if you want to sell tickets.