Not much to hike in northern Maine. Got a canoe? Hop on the St. John River -- a zero portage 5-6 day float along the northern spine of Maine. Two quasi Class III rapids along the way, otherwise easy Class II. A great trip, some white water, wild life, etc., but mostly a long cruise. Easiest way is to pay an outfitter to shuttle a car.
It's a runoff river -- so the season is short -- early-May to early June (just after ice-out is best, to beat the bugs).
Given the warm weather, the river may open early.