The Quebec Dream is boondoggle of itself , connecting New Hampshire and Maine to New York and DC via a one seat ride is a huge economic boost and through Running the T would fix traffic congestion throughout the region. Its well worth the cost , your region is broken transit wise this would fix some of it...
I'm just using it as an example... I don't think Quebec City is worth the investment at all. I just can't see a N/S rail link project being worth it to connect New York and DC to Maine and NH alone.
Do you really think that connecting in Boston (with a direct light rail line from South to North Station) as opposed to a non-stop ride would deter that many people from taking rail to Maine or NH? And what about when they get there? Outside of downtown Portland, is there really much one can do without a car? If they're coming up from D.C. or NYC, it's certainly not a day trip.
I consider Maine and NH to be a lot like Cape Cod. Most visitors to Maine and NH are going to choose to drive because they're family vacation spots and you need a car to see most of the sites. I can't imagine packing my family in New Jersey into a car to drive to the Amtrak station that's closest, loading all of the luggage and kids onto a train and heading to Maine for a long weekend. Maine's close enough to DC or NY that driving is almost as cost effective and certainly more convenient. And unlike Cape Cod, attractions in Maine and NH are much further spread out so connecting them via bus is almost impossible.
Of course, I reserve final judgment for when I see a price tag. If it's even remotely reasonable it'll be worth it. However, I can't see it being less than a few Billion in which case a light rail line connecting the two stations is a far better alternative.