Rumor has it that Pet/Wanda's gonna be played sejak Emily Browning, but there's been no official confirmation. I think it's supposed to be "una surprisa."
Pet will be played sejak an actress named Emily Browning.
If anda want to see some pictures of her playing Pet, anda should check out Us Magazine's collector's edition of The Host. It features some exclusive foto-foto of Emily Browning as Pet.