Temps will stay on the cool side until early May. Considering such a post Memorial Day departure might be best.
Green Mountains are a must see. Coast Maine and Acadia National Park also. There's also campground just across the border about on the Bay of Fundy I've had on my list for a few years. Herring Cove Provincial Park.
Campobello Island North of the border from Maine you could start by visiting Quebec City, Montreal, Ottawa and Toronto. All are about a day drive apart. West and north of Toronto the population per square kilometer thins out pretty quick and your choices of remote back country is pretty much endless. I've most hit the Provincial parks in Ontario with no problems. Haven't looped Superior as yet only Huron.
2006 Hurricane 31D built on a 2006 Ford F53