Are you pitching this as a corridor type service, with multiple dailies, or as a single daily, ala Lake Shore Limited / Adirondack? The communities out there are small enough that I don't think you can justify more than a single daily. Further, from Albany to Toronto, you'd be duplicating both the Empire Service and the Maple Leaf, from Buffalo to Boston the Lake Shore Limited. Basically... I see Albany as a much more viable connection point. I don't see a market for a one seat ride to Boston, justifying a NY/Boston split in Albany like the LSL does, nor do I know if Maple Leaf/ LSL timings work to make connections feasible. That said, I do think EW rail should have BOS-Albany as a goal, instead of Pittsfield.Springfield should be a connection point for two routes to Canada. Boston-Toronto, which could hit a lot of other medium to large cities on the way. buffalo, Rochester, Syracuse, Utica, Schenectady, Albany, Pittsfield, Worcester, Framingham. The other would be a secondary NYC to Montreal route through Connecticut and Vermont. I think it makes a lot more sense for a Boston-Montreal route to go the more direct route from Boston to Montreal through Manchester and Concord. Perhaps it is crazy to think NH would support it. It would probably be a lot faster but maybe more expensive and environmentally complicated.
Either way building out those lines would give Boston a direct route to Canada by rail to Toronto and two potential connections by rail to get to Montreal in Springfield and Albany, both of which would be way better time wise than the current connection in NYC.
Either way, Boston to Toronto is a travel market I'm not convinced is popular enough to justify building out a rail line to support, even with the intermediate communities. Even in a precovid air travel world, Boston and Toronto was never a high demand route, with ~12 daily flights on 50/76 seat Q400s and CRJs, operated by Delta Connection, AC Jazz, and Encore, with maybe an occasional mainline A320 for summer. in 2019, it did 460k passengers total accounting for both directions, which means about 230k out of Boston. The closest comparable by passenger count I could find in DOT datasets is Pittsburg.