Plan is Paris > Nancy > Somewhere in Provence/Toulouse-ish > Nantes > Paris from the end of July over some of the school holidays
1. How does this sound? What is touring in France like? Only done two tours before and they were from Bristol to Exeter and Bristol > Peaks > Liverpool > Bristol.
2. Does France have a Sustrans equivalent? How should we plan the route?
3. How much would the Eurostar or travel to France be at that time of year? What's the cheapest way? We would probably leave from London.
Basically it's an argument between this and Lejog.
checkout distances and elevation profiles with google earth, not even the tour de france follows a pattern like the one you are suggesting, from north to south and viceversa, distances might be huge because they always use train or airplane transfers for the complete route, anyway it sounds like fun so good luck !