After doing a little more research, reading all your replies, and just thinking about it logically I agree .. I think it was an interesting idea to think of but nothing more, for those Germanic peoples to find their way to America would require nothing short of divine intervention and a long list of good luck and coincidences.
With all this in mind what do you think, realistically, would happen to the Saxons, Jutes, and Angles in the situation I created? Western Rome still exists as a political entity and the former imperial provinces of Briton united as a kingdom.
Would the British kingdom let the Saxons settle on a limited scale as 'federates' or would a long a turbulent history between the German peoples and British kingdom take place?
Could the Saxons, Jutes, and Angles remain on the mainland forging powerful Germanic kingdoms to rival the franks and Rome itself?
What's the situation in Northern Gaul?
If Armorica is still in the same position as OTL then you could Saxon settlement there - an ATL Wessex in place of OTL Brittany sounds interesting.
Jutes would probably assimilate to the Franks along the Rhine since they would have difficulties crossing from the lowlands.
What happens the Angles would depend on several factors but since they came primarily via sea then possibly leapfrogging the Western Saxons and doing a Viking to Southern Gaul / Northern Hispania