I've heard parking at the Via station in Dorval is pretty good. It's cheaper than park'n'fly and their shuttle runs often - based on what I've been told. It's right off the exit from the 20 so I plan to use it when I fly out of YUL in 3 weeks. I've use park'n'fly in the past. You might want to call them and look into it. I generally take the 40 onto the island and cross down to the 20 at some point - not specific but I haven't found much difference between the few exits I've tried.

What do you mean "the long way" to BKK? In my experience the flight times east or west are usually similar - what route are you taking and what's the travel time? When you got the ticket you couldn't do a YOW departure? Just curious....