I can see how Kaya could to either way with pronunciation. On one hand, it's not far from
Maya, so it could be MY-uh. But it's also not far from Taya,
Kayla, and words like day, stay, okay, etc. So it could be KAY-uh.
As for KAH-ya, that sounds really close to KY-uh and I don't know why anyone would intuitively say KAH-ya.
I think both
Kaia and Kaya look trendy.
If I met someone with that name, I would not assume a spelling. I'd ask.