I don't know if easter is the same in France but it is early this year. Which is why I booked the ferry on the 27th March. I am not sure if the French celebrate like the Spanish but you may find it has an impact on the aires. Also check that they are open then. I am know many close in the winter but I am not sure of the dates. To be sure of a space especially if you are chasing hookup.......which is surprisingly available in some aires, make sure you are there early afternoon. By about 6.00 all the spaces would normally be full.
Having said that last year I stayed in a beautiful small aire ( enclosed by a hedge) and it normally accommodates 9 vans, one night there were 13!!! that's the French for you.
Bon voyage et bon vacances.