You can pretty much smoke weed almost anywhere in Maine.
There are of course, a few exceptions. But I'll tell you, since the laws around cannabis changed so much over the last few years, it's interesting to see how far people want to push the boundary of what's acceptable. You'll see folks on social media constantly asking about potential drug tests for certain jobs, or what they can get away with on probation... Which you can totally do that now, by the way.
It's funny how our Canadian friends to the North are always so respectful. One Cana-dude (See what I did there? Double pun...) on Reddit was headed for a camping trip in Baxter State Park, and wanted to know what the laws were about puffing in the park. Obviously, he understood that we have legal cannabis here, just like in Canada. But could he just puff at will in the Park?
Maine actually has a very specific stance on that subject.
While it's no mystery that Maine legalized cannabis recreationally back in 2016, folks still seem pretty unclear about where they can, and can't, smoke the Devil's Lettuce (I'm kidding... you do you...). But the quickest of Google searches will take you to several sites that will give you the 411 on 420-ing in Maine.
According to IndicaOnline.com, Maine leaves almost no room for broad interpretation of the laws. Check it out...
Using marijuana in any form (smoking, eating, or vaping) isn’t allowed in public places in Maine, including amusement parks, ski resorts, sporting and music venues, state and national parks, campsites, playgrounds, sidewalks and roads, marijuana retail businesses, bars, restaurants and outdoor or rooftop cafes.
I'm not sure how much more clear it can be than that. Of course, as this gentleman from Canada probably well knows... People have certainly been smoking weed for a long time in all of our state and national parks. I'm not saying anyone should or shouldn't, but my guess is you go ahead and do your thing, buddy. Enjoy our fine state.