Do you think there is anyway the US might have intervened in the Texas revolution sparking an early MAW?
If you want a earlier MAW just have the US get involved with one of the 18teens Texas Filibustering Expeditions.
Why not have Texas lose the war of independence. Could the US really sit by in the aftermath?
Just have Martin van Buren be an expansionist and we have that situation. He could get re-elected if all goes well.
In regards to theory of luring the Mexicans into the disputed zone:
Would Santa Anna be that stupid as to fall for something like that.