Stever, here's some sites you might want to look at about Maine:
www.visitmaine.com
www.exploremaine.org/bike
MDI (Mount Desert Island) is where Acadia Nat. Park is located. Bar Harbor is the primary destination for most tourists. Many Hotels, Inns, Motels, a camp ground or two and access to Acadia.
There is an entrance fee to get into the park. It used to be $3.00USD, but it may have been raised to $5.00. I haven't been to the park in almost ten years so I'm not sure of the cost.
I would suggest you reserve accomodations as early as possible because travelers converge upon the area beginning in May; by June rooms are fairly scarce and expensive.
There are a couple of bike shops in town and at least one of them rents bikes.
Since you are an experienced traveler, I'm sure you'll make out just fine. Enjoy your stay.