Well, I don't know a ton about the hack, but here's what I've heard:

TiVo gets their TV listings data from zap2it.com. When the TiVo dials up, it basically just downloads this data and processes it. So, someone figured out how to get the same data directly from the zap2it.com website.

From what it looks like, zap2it doesn't have Canadian listings. But, I imagine there are other websites offering Canadian TV listings. Now, whether these other sites' data could be used for the TiVo, I don't know. You can probably find out more info on the TiVo Underground board. Or, maybe Dylan wants to ring in on the subject. I suspect he knows a little more than me.