It is still very early to say anything about Prince George's faith.
He may grow up to be a Christian, a Buddhist, or even a Muslim; or he may not even adopt any religion at all. No one can decide except himself.
However, for "survival" sake, the Church of England will ensure all future kings to be a Christian through education and regulated reminder that he is to be the Supreme Governor of the Church of England, thus Christianity is the faith he should adopt and defend.
This is very clear during the young Prince George’s christening at the Chapel Royal in St James’s Palace:
Indeed, the Archbishop had chosen in his address to urge George’s parents and godparents to help the future monarch ‘make sure he knows who Jesus is’, imploring: ‘Speak of him, read stories about him. Introduce him in prayer.’
England is now a country of many different faith, seems the controversial statement by the Archbishop 24 hours later is just a show by him to portrait himself as a 'open-minded leader' and to give a non-aggressive image to the Church of England.