Actually those cannons came from the Mataceros wreck, 1741, further down the coast. The "Cannon House" was the base for the operation and they were sunk there during the late 50's early 60's excavation. You can see some of what they found at the museum in Puerto Adventuras.
The man who led the excavation was Pablo ??? and his bust is the one you see on your way from the parking lot to the bay.
If you want to put a cenote/ocean deal together, consider Dive Aventuras. Plus, if you go to do your ocean dives there, you can stop by the museum, which is not only awesome from a historical perspective, but also free (although we left a generous donation).
Their ocean trips leave from the marina are in PA, and I would bet they would pick you up (no guarantees, when we dive with them, we stay in PA) on the way to the centoes, as there are several good one's south of Akumal.