I personally prefer the spelling
Juliana.
Giuliana really only works in places like Italy, where most 'G' names are pronounced with a 'j' sound. Otherwise, you run the risk of people mispronouncing the name with a hard 'g', which doesn't sound good.
I quite like the name on the whole. I don't like
Julia at all (even though it's my mum's name), but
Juliana (or
Giuliana) is much prettier and far less dated.