We do have beta sign-up but we haven't announced a date as of yet, so it's not a situation where there's extra keys floating around.Your best bet is just to register: https://www.ubisoft.com/en-us/game/skull-and-bones/ .
I don't think we can provide an answer on which ship has the largest amount of cannons at this time, but more details will come as we get closer to release.
Thanks for stopping by for a piratical education!