Right now? It'd be a a tough fight with little gained by either side besides renewed hatred. As long as Brythain can keep it's troops supplied they can go toe to toe with them. Which would be difficult for them to maintain in a long continental war.
That said, the Aurlings have a major advantage that the Frank's don't, namely that they don't break apart their kingdom like idiots just so the royal heirs can all have a piece. That's something that the lesser princes in Brythain do, but Artos, the only surviving son of Arthur after the strife of Camlan, established agnatic primogenitor for the Aurling Luîth(clan)