Oh, I've heard this track before. From what I can hear though, this sounds like it was possibly live recorded, since it's more authentic with how it's played. With that said, it'll be hard to find an exact match in terms of tone, but it's definitely an angelic voice, so perhaps look into children's choir?
Arva, Genesis and even the children's choir in Metropolis Ark are some of the most recommended suggestions. Liberis by 8dio sounds great too, but it's not the most playable or consistent. A women's choir can also do the trick, but it's harder to find one with a more angelic touch to it.