I'm not sure if your weapon affects your cannons accuracy and damage.
But, you should definitely not cannon until your ranged level is much higher, or else you are just wasted tons of money. I've never cannoned at 7 ranged, but I imagine you don't hit very high, nor very often.
Cannons are often considered to be a supplement to a primary weapon or fighting method. This is not hindered or affected by the combat style a player uses. Even more so, it seems to be the case that the accuracy of the cannon is dependent on accuracy of the player's current used attack style stats/bonus (be it Magic, Melee: stab/slash/crush, or Ranged).

