A bicycle is an excellent means of enjoying Montreal's excellent street culture and navigating the relatively compact area covered by the jazz festival. The city's bike infrastructure is extensive and well established. You don't even have to rent a bicycle; use the Bixi bicycle share program to get around.
Stroll Ste Catherine
Take any random night of the festival and walk along Ste. Catherine St. You'll waft in and out of street theaters, art displays and dozens of concerts. It's as magical as Montreal gets.