I would take my car instead of going thru the hassle of renting a car. Depending on where you stay in Montreal, parking may or may not be a problem. I would drive up I-87 to Pont Champlain, which takes you right into the city - not difficult if you avoid rush hour. If you stay at a downtown chain hotel, they offer on site parking, though it's not cheap. If you stay in the old city parking may be a hassle depending on the hotel. If you stay at a b&b or small hotel in the Plateau area, free parking is usually available on the street. Either way, once in the city, leave your car and walk, bike or Metro around the city. However compared to other large cities, Montreal is not too bad for driving.
The drive from Montreal to QC is very easy, if a bit boring. In QC, some hotels and b&b's offer on site parking. QC is quite small and walkable. On the way back, you might want to explore Quebec's countryside along route 10. Magog is a very pleasant lakeside resorty town, Bromont is a ski town near Quebec's wine country. Driving in Quebec is very easy - however no right on red in Montreal!

You can't leave a car that you rent in the US in Canada.
You can take an early morning train into NYP and take the 69 Adirondack to Montreal. The fare (not using Acela) would be $69 per person.
Take ViaRail to Quebec. If you wanted to go as far as Toronto you could take the Amtrak Maple Leaf back to NYP.

Thanks for the info, zootsi. Your posts are always helpful.

Thanks, Tom. We were looking into taking the train.

ACC,

Have you looked into flying open-jaw Philly-Montreal and then QC-Philly (assuming the route is covered) with VIA Rail MTL-QC? You're talking a fair distance to cover by road or rail from home to Quebec and it mightn't be the best use of your time if you're travel window is just a week.

Just a thought

u

If you take a train or fly into Montreal, there is a bus that goes between the two cities on a frequent basis. I've visited both cities without a car, and have been fine. It depends on what you want to do on your trip.