The US just releases a public statement that says they value their alliance with Mexico and have no intention of interfering with their politics or their military.
Texas has Austin, Dallas, and oil. All three are things we'd like to keep; the first two are mainly dragged down by the rest of the state, and the rest of the US still needs the last, for now.
Well the US would have to "Come and take [the cannon]" first as it's in a museum in Gonzales, Texas. It was too much trouble for a dinky little cannon then, it'll be too much trouble for a dinky little cannon in this hypothetical future.
Edit: upon further research the "Come and take it" cannon was not that little one in the museum, but a larger one. However that one was melted down and turned in to a church bell