To my mind, the ideal split would be: English east coast, French in the Mississippi-Missouri basin; and a west coast divvied up between Spain and Russia. These can either still be under rule from the mother country, or have rebelled and become independent entities (a la the 13 Colonies or the rest of Spanish America). But with a POD in the mid to late 18th century, make it that the OTL U.S. of A does not stretch "from sea to shining sea".