Welcome to Boston! I wish I was still at my computer so I could write something more exhaustive with all my recommendations but I second literally everything ATF said!
Little Donkey In Cambridge just opened up and is getting awesome reviews (Asian seafood fusion).
Please go to Tiger Mama, it’s SO GOOD!
Other brunch favorites: the buttery in the south end, tremont 647, and if you do go to Flour bakery get the sugar brioche — it’s like a donut muffin and it’s insane! Also, blackbird donuts in the south end.
I didn’t catch where in Maine you’re going but if it’s Portland let me know and I have a ton of recs because I was just there this week! Short list: duckfat (must get poutine and save room for donut holes), the holy donut, Fore Street (hard to get a reservation), central provisions, SurLie, eventide (for lobster rolls), gorgeous gelato and gelato fiasco!