As to your proposed itinerary:

I've been to Canada many times, and to Nova Scotia on vacation with my family the last two years. Here's what I'd suggest.

Go first to Montreal. Best route is to catch the "Adirondack" from New York. Great scenery most of the way, and a 5:30 pm arrival in Montreal. Stay near the station. I'd recommend the Marriott Chateau Champlain, one block from the train station (ask for a room with a view of Mount Royal), but the Queen Elizabeth (on top of the station) and the Hilton Bonaventure (across the street) are also possibilities. Plan to spend a day in Montreal. It's a great city, and with the Canadian dollar at US $0.66, very cheap.

Take a morning train to Quebec, which is also worth a visit. If you want to stay overnight, the standout choice is the Chateau Frontenac, but it's pricey. Stay in the "Old City", inside the city walls, though.

You can board the "Ocean" in Charny, across the river from Quebec, at 10 p.m. (VIA provides taxi service from Gare Palais in Quebec). It will arrive at about 4 the next afternoon in Halifax. Rent a car and head for Cape Breton Island. Nice scenery and lots of places to stay there.

For a return, I'd suggest dropping the car in Yarmouth (south end of Nova Scotia) and taking the "Scotia Prince" to Portland, ME. By September, there will be train service between Portland and Boston (I hope) and you can go home that way.

Enjoy the trip. French Canada and Nova Scotia are both wonderful places.