The St.Lazare area (where I live) used to have some great trails off of Harwood in whats called the Chaline Valley. I havent been there is at least 5 years and dont know how accessable it is now. Probably your best bet would be to go to Papineau Labelle. Its a nature reserve where you can go camping, fishing, huting, canoeing, you name it. The place is thousands of acres big and there are trails all over the place. You have to pay a small fee for access but its something like 10 or 20 bucks. If you want to camp over night its a bit extra. The place is within 2 hrs drive of montreal and is absolutely beautiful. I wouldnt show up and say " I'm here to off road" as that comes with a lot baggage. Just say your there to camp, explore and enjoy nature, which is completely true. Heres a link to the site.
Im actually getting back into wheeling as I am currently shopping for a 2013 JKUR and have my trusty old lifted XJ to beat on. I was thinking about getting in contact with a few of the local and near by clubs and possibly trying to organize a group trip to Papineau Labelle. I'd like to work with the nature reserve and possibly try to create a charity or clean up event. Still very much in the planning stage, but we will see what developes.
Anyways, Papineau Labelle will provide you with everything your offroading heart desires. Check it out.