Beautiful part of the world. I did that "Loire a velo" route about 3 years ago, from Nantes to Orleans. I'm sure I passed through Monteaux, even though it's not part of the official route. Reason being the bit by Monteaux is flat, while the official route takes you up a hill to the south of Amboise for no apparent reason other than to give a descent back down to the river!
Just home yesterday from France. This time it was St. Malo to Caen, via Granville, Barneville Carteret, Barfleur, Carentan, and Bayeux. Another excellent route with quiet, well surfaced roads.