I honestly thought it was Alyson Stoner. Part of that could have been the Xion theme playing in the background though. It's definitely not Mandy Moore's dialogue from the original game, that's for sure.
But man, I am so happy that the US trailers are getting so much better nowadays! I think they've learned that they can't just do a copy and paste of the Japanese trailer and put in English dubbing anymore. They have to build a new trailer from scratch.
And I just love those Station of Awakening-themed transitions and Destati playing in the background. This was a really awesome trailer!
I actually thought it was Alyson as well
Now I'm really curious though when people get to Traverse Town if Aerith's voice is the same or not? I can't get the game for another week, so I can't find out for myself just yet.