Look for a copy of
River Horse by William Least Heat-Moon. He had the same notion you have now, so he obtained a 22' motorized vessel and, accompanied by various companions along the way, traversed some 5000 miles from
New York Harbor to Astoria,
Oregon.
Don't kid yourself, though. The journey is impossible without portaging often, thanks to the seemingly endless efforts of the Army Corps of Engineers to put a dam on every wild river in the west.
Try here:
Amazon.com: River-Horse: A Voyage Across America (0046442636261): William Least Heat-Moon: Books
TaoJones