Late August in northeast US / Canada

We were planning on going to the Netherlands this summer, but I think we might switch gears and stick closer to home (mostly because flight costs are wayyy higher than I hoped - like $1k/person for basic economy- and just getting more expensive).

We're in Boston and want to stay within a 4-5 hour drive or maybe a quick / cheap flight. This would be late August / early September. I feel like we've done all the obvious places already - our most recent trips were to Cape Cod, Portland ME, Camden ME, Mystic CT, Montreal, and NYC.

It would be my husband and I, our 4 year old, and maybe my mother-in-law.

Where would you go in summer? I want this to feel somewhat special because this is also for my 40th birthday. But nothing is really calling to me. I'm looking at Boothbay Harbor ME, Acadia / Bar Harbor, maybe Halifax Nova Scotia or Chicago or somewhere in Vermont? Any ideas?!