I agree that finding campgrounds in New England past mid-October is pretty hard. Expect some freezing temperatures at night and possibly during the days; you should be OK if your motorhome is equipped for subfreezing use with heated wet bays etc. Snows in October are certainly not unheard of—I remember one rather significant storm quite a few years ago on Columbus day weekend that caused minor havoc with the many leaf peeping tourists and tour busses going around.
Crossing into Canada is entirely doable provided you have the proper identification documents and other paperwork, don't have any banned items, etc. It is helpful, though certainly not at all essential, to have some understanding of French when traveling through Quebec province. A friendly attitude and a little creativity generally will bridge over the gaps sufficiently to get a good meal in a restaurant or whatever.