You can be a member of whatever religion you like in both countries. Since it is an established religion go for it. Hard to find any religious cent res for it but I'm sure there are some around.
You don't need to have Amaterasu or Mount Fuji to worship the Jami. Shinto has no binding set of dogma, no holiest place for worshipers, no person or Jami deemed holiest, and no defined set of prayers. So technically, it can be practiced anywhere.