There is a sports betting bill (which would also allow online betting) before the Legislature as of 2019, but it’s hard to say whether or not that will pass.
While the state is home to two land casinos which can offer the full range of gambling options (with exception to sports betting) and one racetrack, it seems that they are quite satisfied not to expand beyond that. Short Summary: Maine is a pretty moderate state in most regards, and gambling is no exception.