If you're going to be car free I think you're right on the money with your desire to own two bikes. Absolutely take your Cervelo! Alternately, you can buy a bike over there - it's not like there are no bike companies in France. Get one you can't get over here like Canyon or something. I don't know that UPS would be more expensive than checking a third bag on an airline, but you can easily check that out.

I also agree that you should pick up a town-bike when you get there.

Sounds like a fabulous trip!