Like most anywhere, needing reservations in New England is more a matter of when and where you are than an overall blanket requirement. During foliage season and holidays and possibly summer vacation weekends they are advisable, particularly at popular campgrounds.
Quebec gets its fair share of non-French speaking tourists and somehow they manage to put up with them. You should be able to get by; virtually everybody can speak and understand English, certainly those who you're likely to make contact with. Road signage is in French only, but most things are fairly straightforward to figure out. (For example, a red octagonal sign with Arrête means you should come to a complete stop, and it's clear enough without knowing the French.)
Do of course be aware of the border crossing requirements for Canada and the US. It's not a big problem in general, but you do need to be aware of the paperwork/ID requirements (more for reentry into the US) and the regulations on what may be brought across the border (e.g. Canadian gun laws if you carry a gun).
By and large, northern New England is a fair amount more rural than southern New England. I certainly wouldn't consider the north woods of Maine (for example) to be crowded in any sense of the word. Boston, on the other hand....
