As an idea, Boston-Montreal makes a lot of sense-- two cities that rely heavily on tourism dollars, both centers of culture and commerce in their respective regions, a fair amount of bus and auto traffic between the two, and an ROW that hits some interesting spots in between (ski country, a few colleges)...
But as a workable plan, there's just so much money that needs to be sunk into going from idea to steel wheels, there's little chance Amtrak, state governments or Canadian government would go for it.
I will toss this out there: If I were a bored billionaire looking to sell privately owned rail transportation to the United States (paging Richard Branson), this would be one of a few routes I'd think about as a candidate for a pilot program (others, off the top of my head, being Florida, Texas, and the Mid-South-- the corridors that time hath forgot)