Rosamund Pike (Cersei Lannister)

Besides looking perfect for the role of Cersei, Rosamund Pike's chilling performance as a wife willing to frame her husband in Gone Girl prepared her to portray the beautiful yet cold-hearted queen. Pike was also (literally) icy in Die Another Day as a double agent who romanced and deceived James Bond in a palace made of ice.
Nathan O'Toole (Joffrey Baratheon)
Kiernan Shipka (Sansa Stark)
Ed Speleers (Theon Greyjoy)

On Downton Abbey, Ed Speleers played a young man who appeared to be an upstanding person but was devilish just beneath the surface. This acting experience would undoubtedly be helpful for the role of Theon Greyjoy, who is continually conflicted about his loyalties.
Sarah Bolger (Margaery Tyrell)
Jared Gilmore (Brandon Stark)
Jordan Prentice (Tyrion Lannister)
Isobelle Molloy (Arya Stark)
Lily James (Daenerys Targaryen)

With experience as riches-to-rags-to-riches Ella in Disney's Cinderella, Lily James is perfect to portray the good-hearted Daenerys. As Elizabeth in Pride, Prejudice and Zombies James fought zombies, which is exceptional practice for conquering Daenerys's many enemies. Oh, and of course, she's gorgeous.
Augustus Prew (Jon Snow)

Augustus Prew has a long list of TV and film credits, including the show The Borgias. This young Englishman also has the most important features needed to depict Jon: wavy dark hair and rugged good looks.
(Snow image via Facebook)
