Yes, I will do my research, but what are you Fodorites thoughts as to transport to/fro NYC? We could go NYC-Montreal-Quebec-Boston-NYC via Amtrak or take one of the (many) cruises available for the same itinerary. Of all cities, we may forfeit Montreal. Was last to Quebec probably at age 8! It seems that the cruises take longer, obviously they include Newfoundland and few others (Halifax); we've been to Bar Harbor recently so that holds no charm at this point. But havent been to Boston in 20 years, so want a night or two there before returning to NYC. Obviously if a cruise, we'd have to or from Montreal/Quebec as they are one way. Advantages of each in your wise opinions???

Where is home and what month do you plan to travel? The only Amtrak connection is from Montreal to New York Penn station. I don't know anything about cruises starting in Canada.
If you want to take the Adirondack from Montreal to New York then you can take one of the Northeast Corridor trains to Boston South station (or Back Bay).
You could fly to Quebec City or Montreal to start your trip. The passenger rail system in Canada is ViaRail .

Thinking last half of Sept/first half of October, not for a month obviously, probably week maximum but would need longer on cruisehip, most trips are 10 days minimum. We are in northeast Jersey, close to Penn Station NYC, so familiar with rail lines to/fro Canada and looping back through Boston. Seen several options for cruises, obviously takiing longer to round Newfoundland and south. The one advantage of train travel is staying as long as you wish in a city, rather than just an 8-5 day that cruiselines offer.

Here is a loop that might work for you. Take a Northeast Corridor train to Boston. Spend at least 2 days in Boston. Fly from Boston to Halifax NS. The ViaRail Ocean train leaves Halifax on Wednesday, Friday and Sunday. The train #15 leaves Halifax at 1300 (1:00PM Atlantic Time) and arrives in Montreal about 23 hours later. (about 11AM Eastern Time). The coach fare is about $150CAD. The 2 person sleeper is about $600CAD. If you want to go to Quebec City, take a different daily train from Montreal.
You have to come back to Montreal to get the Amtrak Adirondack to New York Penn. If you really enjoy train travel, you could take a ViaRail train to Toronto and the Amtrak Maple Leaf via Niagara Falls to get back to New York.

I'd do the train option to give yourself several days in the cities you want to visit.
The Amtrak Adirondack line is very scenic (but a long ride!). In past years there have been trains with the Great dome car on some dates in the fall but I don't see that listed for 2019.

Now it looks like we will skip Boston (we can train or drive directly to/fro another time) as the train ride there is very long and only through Montreal; DH says no to cruise so looks like we'll do Montreal/Quebec (thinking Hotel Vieux in QC) and leave it at that.