It's a little known fact that, as well as establishing themselves in Britain, the Saxons also had a small, short-lived presence in Gaul, evident from the existence of Saxon Shore forts on both sides of the Channel and from records dating to the fifth century detailing Saxon raids as far south as the Bay of Biscay.
So what if more Saxons arrived in Gaul than our timeline and their fleeting presence there became permanent, conquering the Kingdom of the Soissons and displacing the Franks to establish themselves as the main Germanic people in northern Gaul?
What would the impact of this be?
Would this Saxon territory in Gaul be considered part of England, or would the differences between Britain and Gaul mean that it is considered separate from the start? Furthermore, would any Saxon presence in Gaul be a single unit (i.e. like the Franks in our timeline) or would it be divided between several kingdoms, much like the Saxons (and Angles and Jutes) in England?