Off the top of my head, more recent ish bands that never really crossed the border: The Arkells, Metric, July Talk, Broken Social Scene, Billy Talent, Tegan and Sarah, and many more. These bands sell out large music venues domestically, but can't gain much cross-border traction. They basically are able to exist because of Canadian Content laws.

Oh shit, forgot about Arkells. My wife went to high school with the bass player.

Some other noteworthy ones include: Neil Young, Leonard Cohen, Bryan Adams, Barenaked Ladies and The Tragically Hip.

Of course one shouldn't forget what is perhaps Canada's greatest contribution to music: Nickelback.