Tim would probably know better but there is a difference between a circus which usually has clowns and a carnival which usually doesn't. Carnivals use clown images quite frequently but rarely do they have actual clowns. The clowns would slow down the action of a carnival and a carnival exists solely to empty the pockets of the patrons as quickly and as unobtrusively as possible (in some ways similar to the government.)
Your revised character ideas fit well with the typical Carny. They lead a rough life, always moving from town to town and generally thought little of. The barkers for the different carnival games need to be charismatic and outgoing (which would fit with your "crazy (in a good way) sense of humour" but they still need to be tough to handle themselves in some of the more "unpleasant" situations they run across.
In this day and age I would expect that most cannons are air powered. Explosives would be too dangerous (and loud) and while mechanicals (springs and such) would be possible I think that compressed air, or some sort of piston would be the most reliable and safe.
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