Hmmm, I have it, we revert to conditions pre-1776, but with a change in power structure. Britain (minus various parts of it which may choose not to follow along) becomes the 51st State in the USA (ahead of Puerto Rico, so GB will still have some claim to greatness).
The US then sends all the Mexicans, Muslims (Jews, Gypsies, Indians who are not software engineers …, Native Americans who protest too much about treaties and land and water and such, …) across the Atlantic to the isles formerly known as British. All the white British are welcomed with open arms and offered jobs as Wall-watchers, agricultural laborers, custodians, cooks, gardeners and Trump hotel-maids.
Win, win, win!