If you want to plan your own rides, here are some maps and cue sheets to do it. I did not create any of these.
From the Maine DOT and East Coast Greenway websites
Bike Tours East Coast Greenway from Portland to Brunswick
Bike Tour of Portland, Maine Lighthouses
Bike Tour around Merrymeeting Bay
Round about Century 100.7 miles
Touring around Feeport, Maine
Touring to see Harpswell's Fine Arts and Crafts