Jake Feener, a Maine canoeist has just put out a nice video of a canoe trip down the Machias River in eastern Maine. Some poling, white water and campfire scenes, nicely filmed and edited.
I want to do this trip. I was looking at the route on my gazetteer and it looks like there are a number of roads you can use to adjust the length of the trip.
Yes, it's a great route and not very high traffic. It's best done in the spring because the water gets pretty low in the summer. I did it from Fourth Machias Lake to the coast in May of 2014, and have some notes and photos if they would be helpful. I highly recommend the AMC Maine Rivers guide.