IF I was making a SWAG, I would say that it's what we call a FIESTA CANNON in South TX & Latin America. = According to the curator of The American History Museum in WDC, Fiesta Cannons were generally 18-30 inches in overall length, roughly cast of iron (rather than bronze, brass or steel), have "relatively large touch-holes" and seldom greater than 3 inch bore. Such cannons were NOT designed to be used as artillery; instead, they were designed to fire salutes in holidays.
(The REAL Gonzales Cannon, used in the skirmish of 1835 in TX, was originally a Fiesta cannon, btw. It was made in the late 18th Century in Spain and is approximately a ONE POUNDER, by bore size.)
According to the curator, MANY (but by no means all) such guns were marked on the muzzle with a manufacturer's code that indicated the foundry, date of casting, recommended charge, etc.
Furthermore, Fiesta cannons were frequently "sized" by the pounds of WATER that the barrel would hold, as they were not designed for firing projectiles.
yours, satx