Hi AliClementine,

I believe there is a bus from Bangor, Maine to Saint John, New Brunswick, and I believe that this is the ONLY bus from Maine into Canada. Saint John, NB is many (a full day's driving) hours drive from Montreal/Quebec City staying within Canada.

There are two regular passenger buses out of Montreal to the States... Greyhound to Boston and Greyhound to New York City... that's it. One train: Amtrak Montreal to New York City. Sadly, there's nothing States-bound directly out of Quebec City (which may have been what tempted you as Quebec City is closer than Montreal to Maine).

The Greyhound to Boston is going more the right way and border checks tend to be a bit faster than the New York route, so I'd probably pick that one if anything...get off at Burlington, Vermont (let's say 2 1/2 hours if the border check goes relatively smoothly) and have a cab pick you up there to a car rental place in that town. Then you're looking at maybe 3 or more hours depending where you want to go in Maine.

Honestly, without your own vehicle, it's hardly the pop-in-pop-out deal you're seeking; you're looking at a full 7-8 hours travel each way (as I must include getting to the bus station, waiting on line in Montreal, getting to car rental place, etc...). For a day (!) or two, not to be a spoil-sport, but in my opinion, too much of a hassle for what it's worth.

If you're looking for a two-day getaway, maybe Burlington and surrounding northern Vermont would be a feasible option if you're set on going to the States. Nearby eastern Ontario has some lovely parts too, and you wouldn't have to deal with muck-i-dee-muck of the US and Canadian border. Honestly, with a week, Montreal and Quebec City and environs truly have more than enough to keep even the most go-go-go travellers happy.

Enjoy whatever you decide, Daniel

Getting to Maine without a vehicle from either city will be a hassle. April is not the best month weather-wise for Maine. With a week, I'd concentrate on Montreal and Quebec City. You could easily fill a week with these two great cities.
ps - bring some warm clothing - early April is still wintery in these parts!

If you are Canadian, it is no problem to rent a car in either Quebec or Montreal and drive to Maine if you are returning across the border.
A year ago we rented in Quebec and dropped at Montreal via Vermont.
If you are American, it may be problematic, as you may be perceived to be smuggling the rental into the US.

Having said that, I agree with zootsi that your itinerary sounds optomistic, given travel times.