Assumming that the parts of Mexico taken in the Mexican-American War and the Gasden Purchase were sucsessfully Americanized, were there other states in Mexico that may have been sucsessfully incorporated into the USA.
For instance all of Baja California.
I always found it curious that what is now Arizona was never extended to the Sea of Cortez (the Puerto Peñasco area). Perhaps the Americans didn’t want to over ndulge?
Baja California at that time was barely inhabited. Texas and California were the main prizes. They were seen as potentially valuable and rather underpopulated regions. Arizona and New Mexico only happened to be between the two, at the time, few Americans appreciated the desert southwest at all, or even the great plains.
There were some people who argued for a total incorporation of Mexico after 1848; either as a territory or some sort of associated state under U.S. control - a sort of protectorate. But for Americans at that time, manifest destiny was popular but outright European style colonialism was distasteful. I think the American leadership settled on taking what they saw as valuable but thinly unpopulated lands.
If the resulting border were not so awkward, perhaps they would have even considered leaving the core of New Mexico along the Rio Grande with Mexico, as it was more heavily settled by Spaniards and Mexicans. But we would have had a long strip of Mexican territory jutting into the United States, sort of a Mexican panhandle,
Likewise Baja California would have been an awkward American appendage along the Mexican coast. Regardless of the outcome, I think American statesmen desired ‘regular’ borders with Mexico, as with Canada…the bitter disputes between Americans and Canadians and the British are often forgotten, but at that time, another war almost started over the Oregon Territory over the same issues.