"Santiano" is Santa Ana. I heard from someone whow heard from a linguist that it is only fairly recently that English speakers in some regions became able to pronounce a final "a". In many dialects of the 19th century "California" was "Californy", "Sarah" was "Saro", and so "Santa Ana" became "Santiano."

John Sampson, in The Seven Seas Shanty Book, London, 1927, classifies this as a capstan shanty. Concerning its history he wrote:

"The origin of this Shanty is, of course, the Mexican war, and the original song was written to commemorate the victory of General Taylor of the U.S. Army over Santa Anna...but the sympathies of the sailor who first used it as a Shanty were apparently with Santa Anna, so he was made the hero, and the historical positions duly reversed."

I don't know if Sampson has any real evidence of the original version of this Shanty. But merchant crews were sometimes made up of men (usually waep-men, but one suspects occasionally a wif-man would sail) from many different countries. It's tempting, though entirely conjectural, to imagine a British (or Barbadian, Belizian, Bermudan, whatever) shantyman singing a pro-Mexican version as a way of teasing the Americans in the crew.