It all depends on the weather. Central to Eastern France can be very cold in February.
My suggestion would be something like Calais to Poitiers to St Jean de Luz (on the border at Irun) and then across to Valencia via Pamplona and Zaragoza area. The western part of France being nearer the sea is less likely to get sriously cold or snowy, and when i say 'across' to Valencia is more like 'down'
The Futuriste site at jauny Clan near Poitiers is a very good overnight and popular with the Dutch. The Rouletta site at St jean de Luz likewise. Depending on how many miles you fancy in a day, St Jean to Valencia area is do-able in a day, particularly at a weekend without HGV traffic.
This is the route I have used for more than 10 years, except I start from Caen or St Malo and it has been fine.
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