To the US of course. Scenario must have the 'brown beats black' demogeaphic event occur before, say, 1988.
Annex Mexico and the entire Central America in 1915. That's the easiest route to have massive Hispanic immigration to US proper.
You could start by not having so many Mexicans deported during the 1930s and 1950s, especially in the latter as dubbed Operation Wetback.
This is where I think it should start, yes. Perhaps more labor demands during WWII lead to a larger bracero movement? From there, the post-war boom sees many of them send money home and send for their families.
For whatever reason, I find the idea of a large amount of Mexican immigrants in the 50s to be awesome.