If you opt for the long connection and dont want to head downtown (which could be a pain for the reasons stated by others), I would look into heading to the waterfront in Dorval or Pte-Claire which is a max 15 minute cab ride to the airport with little or no traffic. You could sit by the Lake and read a book and relax instead of being stuck inside.
If you're a golfer, you could also head over to the driving range at Golf Dorval (
http://www.golfdorval.com/) which is located near the airport (actually directly to the North West of the airport)