From the brief research I've done the last couple days this cannon appears to be a Portuguese designed cannon. Evidently during the 16th and 17th century they were exploring what we now know as South East Asia including the Phillipines, Indonesia, and even get credit for discovering Australia. Many of these countries made cannons patterned after original portuguese designs. This one seems to me (my observation,opinion) to be closer to the lines of a Europeon Portuguese example than an Asian made one. Google "Portuguese Cannons" , click "images" tab and a lot of these style cannons show up, both Europeon and Asian made models..............................
ZULU> Would it be possible to get a clear close up picture of the vent?
Dewayne