Has the bore been machined or is it as cast ie: rough??
Looks like someone had a pattern and cast a few cannons, the nuts that are holding the carriage together look modern,the saw marks on the wood could indicate age.
If it is made of cast iron I would be hesitant to fire a lead projectile, wads should be no problem.
I am not an expert on cannons but I work with all kinds of metals every day except Saturday and Sunday. Some alloys of cast iron do not handle applied stress very well and tend to fragment.