"Certain props are not allowed within the Convention Space. These include, but are not limited to:
Airsoft or projectile weapons
Live (sharp enough to cut) steel
Props wide enough or long enough to inhibit flow of traffic
Replica weapons that do not comply with state or federal law
Paddles (all varieties—including “yaoi” or “yuri” paddles)
Props which impede personal or public safety"
As long as its not sharp enough to cut you should be fine,
And as for your cannon, you should be fine, just be careful in the hallways, I've had big props before and as long as you keep to open spaces, and as long as it doesn't stop people from walking by, it should be ok.