Wow you and me have similar tastes! I have a Sienna but tbh Alyssa was on the list (and still is if we have a 3rd girl), but when she was born she looked more like a Sienna.
Why dont you take both names to hospital with you and see which feels better when you see her? I never thought I'd get a vibe from a scrunched up newborn who all look the same, but I did!