is called Saguaro Cactus. I am guessing this is the one you refer to as Giant Saguaro. The other, I think mistakenly called Mexican Saguaro, is most likely Pachycereus pringlei
, Mexican Giant Cardon or Elephant Cactus. Using these 2 Latin names, you should be able to find plenty of info (differences/culture) on the web to determine which might have a chance growing where you live. Good luck!!