Hi Mongvis. Cannon Rocks is a great place to fish. I have not speared in Cannon's before but I have speared in the kenton-on-sea area. Regarding Kenton-on-sea you will find some nice bronze bream and other reefer species just outside the launching bay (Sheltering reef).
If you want to spear Cannons contact Nile from big blue(or something like that) charters when you're in Cannon rocks. You will see his ads.
Nile is a nice guy he will show you some great spots.