There isn't really "the Scottish spelling" of any name, really; spelling was flexible, and it's more useful to think of _forms_ of names. In this case, it's not a "Scottish versus English" distinction, but an "older versus newer" one.
Withycombe's The Oxford Dictionary of Christian Names has an entry for Christian (m.), where she says "The name is found from about 1200, but has never been common in this country", and then refers one to the next entry, Christian(a) (f.), which says among other things, "The name Christian ... together with its Latin form Christiana (occasionally Christiania) are found from the end of the 12th C, and are rather commoner than Christina".