I think the thing to remember is that south of the border is some of the coldest (most northerly) terrain in New York, a long way from any major cities; north of the border is some of the warmest land in Quebec, and the close hinterland of Montreal*. At that I'm using an 1830s map to estimate the Canadian tree cover; it could be considerably more open than that.Very informative thanks. That's actually more open than I thought it was although still a fair number of creeks/rivers and a few hills and forests to restrict maneuvers. Not sure how good the roads would be but the railways are likely to be very important.
There are only a couple of "all weather" roads, but yes, the only major supply route options are the rail lines, the St. Lawrence river or the Chambly river.
* A city with about 90,000 people in it; if it were in the US it would rank 10th in size.