You might want to look at the (very long) thread for last year's (not the) Fridays' tour from Caen to Bordeaux. We probably used some of the velo francette route.
My observations of pre-planned routes, even in France, are that navigation is much more difficult than you think it should be, and that even if there are some really good bits of the route there are some which have been designed to suit the local authority rather than the cyclists who might use them. I'd much rather prepare my own route, based on someone else's.