Your cannon looks like Javanese-pre Islamic cetbang cannon from the late Majapahit period (that ended in 1527). Javanese were making cannons from 14 century after as they have mastered mass-production of bronze.
Portuguese came to Indonesian archipelago in 1511, so probably Javanese improved their design under Portuguese influence (or vice versa?).
Decorations look like from the late Majapahit, they look like pre-Islamic period. Islamic period started in 1527.
I think that you have a very valuable piece. Lantaka, somehow similar cannon but not breech loader, was mass produced, however, cetbangs are quite rare, especially decorated like this.
https://en.wikipedia.org/wiki/Cetbang
http://fotosulawesi.blogspot.com/201...-kerajaan.html