The only place in Quebec that I have read about having good backcountry is in the Chic Chocs. I know there is a hut that a snowcat takes people to and then you tour from there. Not sure about day tour access options. The terrain looks to be the real deal though.
Probably not much help though am I? Carry on...
same here. chic-chocs seems to be the place to try getting some... but you may also find good place if you get friends with a snowmobile. heard good stories from this in the laurentians :-)