I just looked into flights to Montreal, out of idle curiosity. The cheapest flights available on Matrix are $270, but that involves flying through Toronto — at which point I think a lot of people would decide just to hang out in Toronto. (It’s $201 round-trip, nonstop, Boston to Toronto.)
If you want a direct flight from Boston to Montreal, it’s $429 and takes just over an hour. Then add 45 minutes to get to Logan by T from Cambridge, an hour to go through security and such in the international terminal at Logan, some time to get through customs in Montreal, and half an hour to get from YUL to the center of the city. Call it four hours, door to door.
You could take a bus, but that’s 7 or 8 hours in the best case, and costs $188. Then 30 minutes to South Station on this side, maybe some hassle at the border, and another half hour on that end. 9.5-10 hours door to door. Your time is worth some money.
You could rent a car and drive there in 5 hours, apparently, plus some time at the border; call it 6 hours in total. I would have expected it to be longer. As for how much this option costs: a moment’s searching on the Budget rent-a-car site yields a car that costs $122.76. That’s for something akin to a Hyundai Accent; it claims to get 38 miles per gallon on the highway, and it’s 300 miles or so to Montreal, and gas is (let’s say) $3.60 a gallon, so that’s another $56 or so. So, like the bus, we’re up to about $180 round-trip.
(Incidentally, the IRS lets you deduct 56 cents per mile for business mileage. Assuming the mileage rate is a decent approximation to the actual cost of driving a mile, driving your own car there and back would cost somewhere north of $300.)
Finally, as far as I can tell, there’s no train going from Boston to Montreal. (And while we’re at it griping about travel difficulties: if you want to take a train or a plane from Boston to Burlington, VT, you’re going to go through New York City first. That makes very little sense to me.)
Shouldn’t it be just as cheap and quick to get to Montreal from Boston as it is to get to Toronto from Boston? Puzzling.