The photos shared from the museum in Malta by Clockwork have been amazing, and the thread and observations on this extremely unusual wood cannon are most intriguing. I would never have imagined cannon or any sort of firearm made of wood or even more surprising, leather!
I think the suggestions of this being a false cannon are most interesting, but am inclined to agree this seems more likely to have been intended for firing 'empty' charge as noted by David.
This cannon seems very well detailed and constructed, and I would think that something created for visual effect would be essentially a mockup intended to appear to be the object intended from a distance. I know that the 'Quaker' guns used during the Civil War' were sometimes just black painted logs, if I recall from some references. It is truly amazing how often ruse and deception were employed in warfare, and an interesting topic in itself.
Some references I found suggested that some wood cannon were used for effect, but were only able to be fired with single shot or very few. The idea of limited charge with loose projectiles would be somewhat feasible in close quarters, but a solid shot with compressed charge seems unlikely.
Maybe the empty charge idea, for perhaps signalling or ceremonial use might be the purpose?
Whatever the case...extremely interesting!!!
All best regards,
Jim