Hi, we (husband and I, Australians) took the Adirondack from Montreal to NYP last October (peak fall colours). Hope you do better than us, it was very disappointing, for the following reasons:
We had to use seats with no view of the outside world at all (maybe 5% vision). Be ready for this. Halfway down each car on both sides are two seats next to a blank wall, so that you cannot see out. The train was fully booked and we were too slow to realise we should sit separately if we didn't want to look at a blank wall for 12 hours.
There was no dome car at all, despite this being advertised.
As the train was packed, I had to queue for over an hour to obtain "food" and drink. This was no easy task on a moving train, there would be some who couldn't manage this. The conductor closed the cafe on several occasions, often for no obvious reason. It will be closed crossing the border, of course, that is understandable. I was lucky, but people 3 spots behind me, who had also queued for an hour were told "bad luck, go away". Anything decent in the way of food sold out immediately, anyway. I would suggest that you bring substantial food yourself, if it matters to you. I thought we would get more than a microwaved burger. At the least we should have been warned at the ticketing desk before leaving. The conductor and his young lady assistant spent the entire hour that I queued chatting happily in a seat in the "cafe" while the cafe assistant worked at 150%. He did a great job and passengers showed their appreciation by tipping. The other two completely ignored the situation, I'm not sure what they did to receive a wage, let alone a tip.
The left side of the train leaving Montreal has great views of lakes (one benefit of queuing for an hour, I saw something) and the right side river views coming into New York, although it could be dark then.
The bathrooms were not user friendly for most of the journey. It is apparently not in the job description of the on-board staff to do anything about this. How hard is it to gather up a plastic bag of paper towel and replace it with an empty one, so that passengers are not knee deep in used paper towel? I leave the smell to your imagination. There is a longer stop at a station about 2 hours outside NY, forget the name, where there is food and toilets available, most passengers queued there for either (or both, if they were really lucky).
Be aware there are no Amtrak ticketing machines in Montreal, you will need to go to the desk. There are some good food outlets there.
One hilarious note, when leaving the train at Penn Station, a lady from Florida, who said she had been to NYC several times, was quite alarmed at the thought of using an escalator. She asked me if I thought it would go up or down! As it seemed to me that we were about as far underground as anyone would want to go, I guessed it would probably go up. She started yelling at her husband about this.
On a happier note, we had further excellent trips on Amtrak to Boston, then to Portland on the Downeaster, so it wasn't all bad. Hope it goes well for you.