A cannon is an outdated artillery piece where a gunpowder charge was used to fire metal balls (and occasionally other stuff) out of a large metal tube. They were often find on sailing ships and in castles/fortresses.
Now canon, on the other hand, which is brought up in many threads around here, is like "official", or "true to the source". If we talk about giving a ship it's "canon" stats, then we're talking about the exact stats that it has in Star Wars. Canon is usually balanced with game requirements, so if a fighter normally has the same shields as a large freighter, then it might get scaled down because that's an insane amount of shielding.
"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."