Sophia becomes Queen of The United Kingdom in the early 18th Century and her son, Frederick the Great unites Prussia and the UK in Political Union.
During the War of Jenkin's Ear, the increase surplus of Prussian ground troops and a lot of disease related luck result in decisive victories for the United Kingdom of Great Britain, Prussia, and Ireland and they dangle Protectorate status in front of dissatisfied Mexican Criollos for rising up against Spain.
Mexico (minus Texas, the Californias, and the Arizona, New Mexico, territories) and some of the Caribbean goes to Anglo-Prussian control and Frederick's Britain sets Mexico up as a penal colony for Prussian convicts and Irish dissidents. Spaniards and Criollos not loyal to the UK travel north to the remaining Spanish portions as well as Louisiana as Mexico becomes decidedly more Anglo-Prussian.
Eventually, after Frederick's earlier death, and after more Germans were being sent to the Northern American states and more Irish and English were being sent to Mexico, the American Revolution occurs due to Frederick's son with Augusta of Saxe-Gotha, King George, being kind of a dick... Meanwhile, the Texas-to-California remnant of New Spain rebels against Spain, but quickly falls apart from lack of foreign support and American filibustering into their sparsely defended territories.
America eventually still gains the Louisiana Purchase and goes to war with the remnant of New Spain for their territories.
America is significantly more German, and with the assimilation of the West, significantly more Spanish, and Mexico remains British.
Good enough?