Ok. One POD: Mexican American War; the US conquers Mexico. How will you get them largely anglicized, to the point at least of how Louisiana was Anglicized OTL.
POD 2: No major war, the US takes advantages of mexican instability and foments a collapse and annexes the republics, then fills them with white americans. spanish speaking whites become americanized. mestizoes and natives immigrate to the great plains decreasing their numbers in mexico. How would you anglicize them? how long will it take?