After Caesar conquered Gallia, Gauls became Gallo-romans: they adopted roman lifestyle but keep their beliefs (druids,..).
Frankish invaders 'd just forced roman legions to go back home

They were not so many. They stayed in the north of (today's) France and mixed with local population (not all the population). Then next french leaders were frankish but just a little part of population too...almost each little part of france had his own language and culture at this time. (It was still the case till the 19th century).
So I think that French are more "gauls"(and celts) than germanic.
This is an excellent website with a lot of europe maps from 0 AD to 2000 AD:
http://www.euratlas.net/sommaire.htm