The only pronounciation I'm aware of it Guy-uh. I read a really good book series about a girl named
Gaia, and she struggled with people mispronouncing it, but I don't know how common that really is.
I can't imagine it being confused with
Kaia. Other than the book character, I don't know any. No idea which celeb used it, so I don't think it'll be popular anytime soon.