Well Adventure cycling has the Lewis and Clarke route,
https://www.adventurecycling.org/rou...k/lewis-clark/
I want to do this route.
There was once an active bike route that ran along the Mississippi and many have done it. Lake Itasca to Iowa is very doable I think. Rains are not long and soaking in the midwest.
https://en.wikipedia.org/wiki/Mississippi_River_Trail
Shouldn't you be busy teaching in September?