I live in Montreal , and work in the old city. For food I recomment these two web sites that will help you tremendously :
http://forums.egullet.org/index.php?showforum=26
http://www.chowhound.com/boards/show/22
The website for Montreal tourism is very good :
http://www.tourisme-montreal.org/B2C/00/default.asp
Now , I dont know if it is your cup of tea , but you will be in town for the last weekend of gay pride and the first Outgames , so there will be a lot of action and a very festive atmosphere. The whole section of town known as The village ( the gay erea) will be closed to trafic and restaurants will spill into the street. Picolo Diavolo and Area are among the good ones.
On sunday , august 6th will be the biggest day , with a giant out door tea dance and a big disco show thet lasts all afternoon in Ameli Gamelin park. It is important to notice that in Montreal , everybody goes to gay pride , not just gay and lesbians.
You have to eat smoked meat at Shwarts ( on the montreal web site) close to pastrami , but much better. And dont you dare take a lean sandwich , go for medium with mustard ! You will die and go to heaven.
If you are serious about food , go to Jean-Talon market on saturday or sunday ( if you choose not to go to GP) It is the biggest farmers market in North America , with a lot of food stalls that sell nibbles from all over the world. A stop at Havre aux glaces (an amazing ice cream store) for italian type ice cream is must. The other must stop should be Marché des saveurs du Québec , wich specialise in artisan food from all over the province. If you like cheeses , youre are in for a treat , since the carry most of the artisan cheeses from the province. There micro brew selection is amazing and you should try ice cider , wich is hard cider made from apple that were left to freeze on the tree. Very good and sweet , especialy with blue cheese ! Marché jean-talon is open all week , but there is more choices to eat during the weekend. Go to Jean-Talon subway station.
Old Montreal is beautifull. Ask your hotel if they have the self guided tour of old Montreal , other wise go to tourist info at Place Jacques Cartier , close to your hotel.
I toured a bit of old Montreal with Raja from the Dis. Obviously , I might be busy during the weekend , but feel free to PM me , we might never know , if I might be to show you around a bit !