I can't help with the rest of the route but let me start by saying that from Niagra Falls to Montreal (or the other way around. in Canada) you pass through Toronto, Ontario...and it's a Pain in the ...well anyway. If you travel that route during any waking hours, the 401 is a red hot mess on week days and not a lot better on weekends. There is a toll road called the 407 and it's a plate reader not a booth toll road. You probably won't get the bill as you are from the US and I don't think they send them there. Not long ago they didn't send them to QUEBEC! AND even if they do send it to you...trust me, it's worth it.
I live just outside of downtown Montreal. There is a campground not far from us that I have visited for a permanent site. It's simple and clean and the staff is great. It's a KOA St Philippe de Laprairie, Quebec Campground | Montreal South KOA
. The highway that is just off of goes south to the 87 in NY, maybe 20 minutes away.
August is a bit busy for me but send me a PM if you know when you will be in town and if I have time maybe I can give you a tour or at least point you in the right direction.