I went to both Toronto and Vancouver on my last trip. After getting through the terrible arsehole customs people in both cities airports, well Vancouver is the better place of the two in my view. I did go in the summer time. Toronto had things like Niagara Falls within a day trip, Toronto Island park which was alright but nothing spectacular and not a great deal more worth visiting. Vancouver had plenty of things in the city, nice nature around the city. Then a bit further afield you have got the Rocky Mountains, which are really nice and worth a visit. It was nice to get the nice fresh clean air in the mountains and to go out in them in normal clothes and not freeze to death like would happen in the winter time. In the winter time I'm sure they would still be good, but I wouldn't like minus 40 degrees celsius like locals said it can reach. Banff is a really nice place which has got things like Lake Louise, Stanley Glacier, Grouse Mountain and many other places close by. It was really nice to get out and experience the mountains (I didn't see any grizzly bears though like I wanted to even when I went in to danger zones for them by myself).
Be warned though if you plan on arriving at the airport in Toronto or Vancouver, be prepared to be treated like a terrorist if you are travelling on your lonesome and have been to plenty of other countries prior to Canada. About the only thing I didn't get done was a strip search, and I make sure I am well presented and clean whenever I go through an airport to try and not get that crap treatment. It's not like I have piercings on my face, tattoos on my head, punk hairstyle or anything that might suggest mental issues or dangerous Osama Bin Ladin stlye person. America wasn't half as bad with treatment through airports as Canada and they have got a bad reputation for dishing up crap to foreigners.