Maybe because Canadians are just milquetoast Americans without handguns?
Actually,
South Park is about the only program I know that makes fun of Canadians. And then it works because few others have bothered to do such a thing. What makes it funny in South Park is that Canadians generally don't give us a whole lot to make fun of.
Most jokes involving Canada or Canadians here involve them being like odd cousins who live in suburban Buffalo, NY. (Though Vinman might dispute.

)