We in the antique arms business call these little, overly-long-trunnioned cannons "decorators." They were made anytime from 1890's to the present. Merchants saw a demand for all kinds of arms, armor, etc. that the noveau riche could hang on their walls, put on little pine carriages, etc. in their big homes to look like they were a part of the old money crowd. Real cannons were too hard to find even then, when a great many were needed, and the fancier the better. The latest ones I've seen had a pseudo-Spanish theme complete with COA, and snaky "rope" designs on the barrel. There have been some pictured on this site.
Please remember that term, "decorator," and use it when appropriate.