I live in Montreal...and while malls and some stores etc... will likely be closed, clubs will be open. There are a lot of big Victoria Wknd parties that happen. ALl you have to do is walk down St. Catherines (the main downtown street) and you WILL see flyers for all the big parties littered on the street and on teh windsheilds of parked cars. If you see ppl passing put flyers, just take one and you'll know the deal. Otherwise, there are some websites you can check out for info on the goings-on. Off the top of my head: <a href="http://www.blueagenda.com" target="_blank">web page</a> <a href="http://www.kili.ca" target="_blank">web page</a> , and <a href="http://www.montrealnightlife.com" target="_blank">web page</a> . Finally, wrt restaurants,call ahead b/c some close on teh monday and some don't. The big happeneing ones, Buono Notte, Meditteraneo, Red Thai, Biddles....will likely be upon but call ahead to be sure.
All in all, Mtl is a great city and public holiday or not, you WILL find stuff to do. If all restaurants are closed, just go to Chinatown where places will be open untill atleast 2AM.
Whew, PM if you want to anything specific.
HAVE FUN!!!