Spain getting Louisiana back probably ushers in the biggest change on the continent. OTL Texas was able to do a 'Texas' because the neighbor to one side was an expansionist US who had easier access to it than Mexico. Texas was rather remote from the populous part of Mexico. It was slow growing from a Mexican POV, which is one of the reasons they invited in the US Americans. New Orleans/Louisiana was a fast growing region in 1800. While US Americans were entering, it was mostly with the blessing of the Spanish/Mexican gov't and reasonably controlled. LA was also getting direct European immigration. While the flavor wasn't exactly Spanish/Mexican, it also wasn't US American. Texas is going to be an extension of that rather than the OTL US American flavor that came in and could be easily persuaded things would be better independent/under the US umbrella. IF Spain/Mexico is in control of the Mississippi, and Texas does try to pull a 'Texas', Spain/Mexico can cut off easy access from the US Americans and send troops to put down a rebellion.
If/when Mexico decides to rebel, LA may decide to remain with Spain. It is way too underpopulated to make a go of it as an independent country, but it may not want to join with Mexico. Plus, if Spain maintains control of New Orleans, it maintains control of Louisiana. Holding St Louis as well also cements Spanish control. Control of those two cities helps Spain manage the US American immigration. Eventually, LA will go the way of virtually all OTL colonies, which means independence. But if it grows up and populates under a Spanish gov't, it will have it's own identity and is less likely to want to join the US, who is also less likely to want to absorb a huge non US entity. This last point also holds for Canada. At some point, Canada will be too strong politically for the US to desire. the US wants populations it can control and assimilate, not foreign entities with political clout it can throw around.