Well, if you're coming sometime soon, you could do some of the fun wintery things Ryllharu talked about in Ontario and Quebec. I believe VIA Rail (the highway robbers of all rail companies) have a pretty good deal for travel within the southern parts of those two provinces if you want to see a lot of the country. Definitely stick to the cities this time of year. Ottawa has a really cool hostel you can stay at that used to be a jail, which is fun.

If you want to visit some of Canada's warmer climes, Vancouver is about equivalent to England in the winter. Cool and rainy, but not really too cold. I think you were referring to the 'Sea to Sky' highway perhaps in your post, which goes from Vancouver up to Whistler. It really is a gorgeous drive, and if you do any skiing or snowboarding, Whistler is a top-notch place to go. You can even just get a pedestrian pass or whatever they call it, and ride the gondola up the mountain to look around, and then ride it back down.