Best route from Harrisburg, Pa to Bar Harbor

Another option is to take I-81 to I-88 to I-87 (via a tiny bit of I-90) and then go across Vermont and New Hampshire. I'd probably do that part taking NY 149 from Lake George to US4, north on VT 22A to US7, I-189 to I-89 to US2 at Montpelier (exit 8), and then probably Alt US 1 to Bar Harbor. This would definitely take longer (and I think be a longer distance as well), but is a more scenic route.

I-88 used to be pretty rough, but the majority of that has been fixed over the past few years.