Citroen C2 vs. C3
 

I'm selecting a rental for Provence in September and am wondering:

Aside from the 2 door/4 door difference between the Citroen C2 and C3 and the fact that the C3 is a bit longer, are there many differences? I know the C3 often comes with GPS and other bells & whistles, so am wondering if the C2 is likely to come with the same or not. The C2 AutoEurope is offering me does not have AC, but I'm hoping that won't be a problem in mid-September.

In Provence, in mid-Sept., you might very well wish you had air conditioning. It can still be quite warm.
The C2 is smaller, of course, but IMHO, also less comfortable. It's a lot harder to keep your luggage out of sight with the C2, if that's a concern. (check this photo:
http://www.topgear.com/drives/A7/A6/gallery/03/
You may find it helpful to go to the www.topgear.com web site and read the reviews of both the C2 and the C3.
I would pick the C3 over the C2 in a minute, but I'd still pick the C2 over an Opel Corsa. However, will you really be able to guarantee you'll get one or the other and not the "or similar"?

C2 is effectibely a 2 seat car if carrying any amount of luggage

You are correct, BT, that it is "or similar," so perhaps this is not entirely my decision anyway.

Our AutoEurope C2 in April turned out to be a Getz (i.e. we got a similar) - did not request or pay for AC but the Getz had it. Made me wonder how many un AC'd rental cars there were. Liked the Getz very much - had to work at keeping all the baggage out of sight but it was do able. Also, go for a diesel, you'll save money on fuel