Except there is no single authority of the English language (as seen in other language academies). As I mentioned in another comment, you may fall into a prescriptivist or descriptivist camp, but there's no authority to which one can appeal for a single answer.

Generally speaking, octopuses is preferred by most if not all well known dictionaries in modern usage, and the pseudo-Latin cognate has fallen out of favor. I don't think it's reflective of reality to argue that all three are equivalently correct.