I live in Halifax, Nova Scotia & will be pleased to tell you all I can about my beautiful province. Boston is about a 16 hour drive from Halifax, and the drive on the I95 into Maine is pretty boaring, although I'm sure there are other more scenic routes.
Since you only have 10 days, I'd suggest flying right into Halifax. There is so much to do here, and you rent a car once you get here to tour around the province. Nova Scotia has beautiful autumns, but I should warn you that spring time usually brings lots of rain. The salt air here smells wonderful, and because geographically the province is long and skinny, you are never more than an hours drive from the ocean.
Some must sees include:
Peggy's Cove -- Just 30 minutes from the city it's a huge tourist attraction. Created during the ice age, it's miles of big smooth rocks that the waves crash up against. I like to go there late at night with a blanket and a bottle of wine just to hear the ocean.
Cape Breton Island -- Famous for it's beautiful highlands, the Cabot trail, Celtic music (Ashley MacIsac, The Rankin Family, Rita MacNeil etc)
Halifax -- one of the oldest cities in North America, Halifax was founded in 1755. It's the largest city in Canada east of Montreal. Halifax is a pretty cool city. It's just big enough to have some culture, but small enough to feel safe walking alone at night. The are five universities in the city which give it a really youthful, alternative feel at times. It also seems like it is becoming a more queer positive space.
It sounds like you like the outdoors. Nova Scotia is a great place for hiking, cycling (although hilly), mountain biking, canoeing. There's also a lesbian outdoors club here. I've never made it to one of their events, but it seems they plan adventurous outings every couple of weeks.