I agree with what the others have said - patricularly Dave's comments about Banff! I also wanted to suggest that if you follow Dave's route, and you're and experienced boarder then definately check out Kicking Horse - some of the most awesome terrain I've ridden, and great off-piste as well.
I spent a season in Banff before heading over to Vancouver. Personally, I liked the Banff/Jasper end of the Rockies better than Whistler. Whistler was just a little too crowded for me.
Which ever you decide on though - you'll have a wonderful, memorable trip.... bring on the powder baby!!
[ Edit: Edited on May 17, 2007, at 9:10 PM by KoalaGirl ]