Bicycling the French coast

Beginning where in France?

See this map with lots of information (in English and French) and the cycling routes from Narbonne to the Spanish border:

https://www.tourisme-pyreneesorientales.com/sites/www.tourisme-pyreneesorientales.com/files/atoms/files/carte_troncon_recto_verso_compressed.pdf

Judy has asked the right question ... which French coast. Mediterranean or Atlantic? Regardless, take a look at

https://en.francevelotourisme.com/cycle-route

and

https://www.freewheelingfrance.com

Are you taking your own bike with you, getting one there, or looking for a guided or self-guided tour?

IF you are looking for a self-guided or guided tour, the freewheelingfrance site is a great starting place.

IF you are on your own, perhaps https://www.komoot.com/guide/536/cycling-in-france, https://www.komoot.com/guide/46594/cycling-in-new-aquitaine and https://www.komoot.com/guide/48934/cycling-in-occitania would be useful. Going into Spain by the Mediterrenean may well involve the Pyrenees and lots of elevation changes. https://www.komoot.com/guide/52489/road-cycling-routes-in-pyrenees-orientales; I have no idea about the Atlantic side.