Shootingstar was actually suggesting West to East, not East to West.

This being said, I'm originally from Montreal, Quebec, and I know many people that rode from Montreal to Vancouver (thus East to West) and who thought it was "nicer" because the most spectacular and (to them) least familiar scenery was at the end. They also had a chance to train for the bigger climb. Prevailing winds are from West to East, but it's not as significant a factor as it is going from B.C. to California (where you really MUST do it from North to South).

Some bits of southern Ontario and Quebec can be a little industrial, and would make a less-exciting end-of-trip. On the other hand, assuming you'll end in the Atlantic provinces if you start in Vancouver, that can also be quite beautiful... and there are serious climbs (although shorter) there, too.

Have a great trip!!