alternatehistory.com

So I found a map the other day where Gran Colombia and the former USA switched fates, in which the USA, instead of dissolving into her constituent states like OTL remained united; while Gran Colombia--or Patria Grande if you will dissolves into several Republics. How realistic is this scenario? I for one do not believe for a moment that the USA, of all nations could have a border on the Rio Grande.
And here's the map:
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