It's impossible to predict the best times for foliage, but you will almost certainly pass through some fantastic foliage and scenery.

With 2-3 days for travel, you can certainly avoid the 4-lane superhighways and travel on some of the smaller roads, where you can enjoy the scenery much more. There are a lot of possibilities, but here's my suggestion for an excellent and easy-to-follow drive that will avoid many of the biggest crowds:

• Day 1: From Boston, go to Route 128 (also called 95) via Mass Pike, Rt 2, or 93 North. Then take 128 to Rt 2 west. Follow 2 west to 495, take 495 North a few miles to Rt 119. This is where the good stuff will begin and continue. Follow 119 West to Fitzwilliam, New Hampshire (in the Monadnock Hills). Then take Rt 12 north all the way to Quechee, Vermont. Stay that night in Quechee, Hanover, or White River Junction.
  
  
• Day 2: From wherever you have stayed, take Route 4 West to Route 100. Then follow 100 North through Waitsfield, Waterbury, and Stowe, then head west on Route 15 to 104 until you reach Interstate 89. This is where the terrain flattens out, and you can head directly north to Montreal.

A big caution: This is an extremely busy time for hotels and B&Bs in New Hampshire and Vermont, especially on weekends. I would strongly advise that you make your reservations now.