What if San Martin had gotten to Upper Peru first and Bolivia instead returned from Lima to Bogota with Peru becoming integrated into Bolivia? Later on, Santo Domingo joins the Republic (as attempted OTL).
Then, before he can become too domineering, Bolivar drops dead (catches a cold and falls off his horse?) and a Confederal Government is established in Gran Colombia
Ultimately the country's boundaries are set at the Purus and Madeira Rivers as well, giving the country much of the Amazon.