Sounds like a great trip. I'll let you know if I hear of anyone looking to get out then.
For routes, I'd suggest avoiding the lower Mersey since it is all dammed up. The Medway, Jordan, and Roseway are all great options and easily accessible from the Shelburne River which I assumed you will paddle down a bit. For white water, the Medway and Roseway take the cake, but for wild-ness, the Jordan is a decent option since it has very few cabins or access points all the way down to Jordan Falls on Highway 103. It has one major section of white water but it is otherwise relatively calm compared to the other two rivers. Another further option is the Clyde, which you would access from the Roseway.
We will soon post downloadable files so paddlers/hikers can have this data on their GPS/phones.
Cheers,
Alain