I would make reservations at any of the below:
I really like Sho-Dan on Metcalf Downtown. The specialty rolls that aren't on the menu are the best! Although not cheap! I do believe it's one of the better known sushi restaurants in Montreal.
I also really like GINGERS for sushi on Pine and St Laurent... If you go try the sushi dessert its AMAZING!
Kaizen sushi bar on St Catherine corner Wood Avenue
Juni: $$$$$ http://www.juni.ca/
Maiko Sushi on Bernard is VERY GOOD! horrible service always....
From the Jazzfest, take the bus north (the 80, 5 minutes) up to Laurier, there, you can go east or west to either "Jun I" or "Mikado"; or closer to the site, there's Zen Ya on Ste-Catherine.
I've been to all of the above, and they all are good, "Jun I" is a notch above the rest IMO.
I like Oishii Sushi (sp.?) which is more or less on the corner of Park Avenue and Bernard. The quality is very good and prices are less than what you'd pay at Kaizen and the like. There's also Jun-I, on Laurier a few blocks east of Park. It has gotten rave reviews and I think has some pretty creative rolls, though I've yet to try it myself.
Note that neither of these restos is really near PDA, though they aren't really far either.