Yeah, depending on where you are, i could tell you a bunch of different place, but im not 100% sure if they all do tours.
Most of the breweries are in the Portland area. I have been wanting to visit Allagash. If you come to my area of the state, theres Black Bear Brewing Co in Orono, Penobscot Bay Brewery in Winterport, and Geaghans Brewery (which JUST opened) which is within walking distance from my house. There are plenty of other fine places as well, but I cant think of them off the top of my head, and Im on my phone, which wont let me easily search.