Few places so close to Montreal can boast as many hiking options as the Eastern Townships.
The numbers really do speak for themselves: Between the 25 summits (that's a euphemism—they're only just over 1,000 meters high), the 4 national parks, and the 500-plus kilometers of hiking trails, just about anyone can create his own day trip itinerary, perhaps with a few winery stops along the way.
I think autumn and winter are best, when the scenery is the most striking. There are even showshoes available for rent. And, Mont-Mégantic is the most famous star-gazing site in the country, with a dedicated center and scientific classes.