I did the eastern section of the Adventure Cycling Northern Tier route several years back and it was an excellent route from PA to Portland, ME. You could pick a section you want to ride near you. The Maine part is particularly nice but there are some hills you will notice. The maps they sell have camping, lodging, bike shops, etc. all indicated nicely like the old AAA Trip Ticks, but a lot nicer and specialized for bikes. Nice low traffic scenic roads too..