As a French, i recommand you the HRP (Pyrenée Hight Route) that crosses the southern part of France between Mediteranean sea and the Atlantic Ocean, on the Spain border.
Pyrenées look like the Sierra sometimes, JMT/PCT got more space and expansive views but Pyrenées really worth it too.
HRP route goes hight on the crest and can be challenging, but not technically difficult.
Resuppluy can be a concern though.
the total hike is about 800km (500 miles) with a good 43,000 metres of elevation gain (143,000 feet), so be prepared...
here is an english link for guidebooks:
you'll need to get the HRP guidebooks by Georges Véron "Haute Randonèe Pyrènèene"
However, to conect Atlantic Ocean to Mediteranean sea, you could take the easier GR10 on the french border side, the trail is well maintained and easy to follow thru "medium elevation mountain".
The Gr11 is pretty much the same on the Spanish side, and the "sentier de Piémont" (france) is a moderate hike with the same goal but with more travelling into the valley and small villages, it's a more cultural experience.
a few good links here for the HRP:
Besides HRP, i would recommand the GR20 (look South -East) in Corsica island, it's a very nice and famous thru-hike, i will try it next summer as a training before my Colorado CDT.
GR20is a stenuous 200 km hike, it can hot in summer, trail is obvious, and you can sleep every night in a shelter or pitch your tent around if it's full, it's a great scenic trail with steanuous elevation gain everyday, hike light!
If you need more info , you can email me, good luck!