Classic fantasy with world building etc. isn't a genre the French wrote much, except in the youth literature category (most of which isn't as good as the anglo-saxon offer), not yet. Most of what come close to Fantasy is better comparable to "magical realism", or else what we call littérature fantastique (ghost stories, supernatural stuff and what not).

Vonarburg is worth checking. She's primarly a SF writer, but her most recent series is alternate history/fantasy in the vein of Guy Gavriel Kay.

Pevel is another.

If you want to check out the catalogue of À Lire, the French Canadian publisher of genre literature, it's alire.com Perhaps something with strike your fancy in there. They carry a mix of original works and foreign works in translation.

Bernard Weber suggested below by jh might interest you. What he does is close to Fantasy/SF, to spec fic at least, and he's an easy read.

I'd second his recommendation of D'Ormesson. It's not fantasy, but he's a very good writer. So is Malouf. Not so easy reads, though.

Some of Messadié maybe. Not Fantasy at all, but some of his novels might appeal to Fantasy fan, like Matthias et le Diable (more "magical realism" and historical novel), or his novelized biography of Comte de Saint-Germain that is quite fun (especially if you liked Foucault's Pendulum).

But the bottomline is probably that's Fantasy isn't really the genre francophones have been best at so far. There's plenty of fun and not to hard to read books in other genres though.