If you have never driven in the Northeast, you are in for a surprise.
Congestion like you've not seen.
Do you need to get to watertown or did you just pick it arbitrarily? If you don't, read below.
I would suggest I84 and get off in Newburgh, pop onto the NYS thruway and get off at I90 going east to Mass Pike, 495 around BOSTON to 95 in maine.
We left Hudson valley area in NY (near Kingston) at 7:30 in the morning (stopped at chipotle along the way for lunch) and arrived in Bangor around 6:30 pm (with stops for cheapest gas along the way). It was a smooth ride the whole way and we didn't hit any nasty rush hour stuff at all. I hate traffic!
Fuel up at the corner of NJ off route 84. Gasbuddy.com check the heat map. Gas is pricey in NY!!!! Parts of MASS are cheap on gas and so is NH. Ge propane before you go over to NS as it can be hard to find (as per someone who lives there but he had an onboard tank, not refillable).