Go here! I've rode my bike here from MTL last year and this year opted for the train into Deux Montagnes and the awesome ride from that point! Both are good options and just depends on how much of your day you want to spend biking and how comfortable your bike seat is!
We did the very short trail (Sentier de la Grande Baie) which ends with an awesome wooden bridge out in the water near la Grande Baie. It was very beautiful and highly recommended! From there we rode to the apple picking places on Chemin Principal and then to Gare Deux Montagnes. A great day trip to escape the city!