A cannon is an outdated artillery piece where a gunpowder charge was used to fire metal balls (and occasionally other stuff) out of a large metal tube.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.
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"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."