For your application, I would go for the AR-7. Floatability is critical here.

I used an AR-7 for years, and liked it a lot. It is a plinking rifle and it is not insanely accurate. I am sure Chris is correct about different barrel tension affecting accuracy, but I could always hit the target. When I introduced my sons to firearms, we used it as a single shot, and I think I would employ it in that manner if I were in a survival situation.

My strategy when kayaking is to prepare for a situation where everything aboard the kayak is lost, and I am left with only what is on me. Therefore I always have liked PFDs with lots of pockets and lash points. I would think seriously about a handgun that you could keep on you if you want to be sure you retain a firearm.

Losing your kayak and its contents is not hypothetical. I was in a group off San Diego in which one of us was dumped by a wave. Said wave surfed his boat quickly out of sight in the rather dense fog and he lost the whoe shebang, including some nice camera gear secured in the rear compartment.