I heard the voices already.
They made a few tests and did cast fans that are as close as possible to the originals. In fact, it was hard for me to hear the differences, although another brony said that he was impressed but the differences would be clearly there^^
However, after hearing the voices, I'm really looking forward to it.
Meredith Sims - VA for Twilight Sparkle
Karen Hayman - VA for Applejack
Kira Buckland - VA for Mayor Mare - Announcer
I'm sorry couldn't find any other source than the first, but they must exist, cause I heard them all.
Ok, found Karen on soundcloud^^