Would be disappointed to see Ambiorix, for reasons previously discussed, but that does seem to be a major possibility. And they sort of already did the same thing Scythia and Tomyris, so I don't exactly have faith.
I think Vercingetorix, despite being the most popular name, would really be the best pick here. Dumnorix would be interesting as well. They are both somewhat Roman-centric choices, in a way, but in terms of unique power and "historical relevance" they seem to be effectively unmatched.
As for the Gallic Emperors, I think that they'd be awkward choices at best. Interesting men, but not any real embodiment of the cultures of Gaul.