Hmm... I could see two ways to do this:
1) As a sort of "mini-game" for the characters. A pastime and something to diverge from the normal campaign sometimes.
2) As a d20 based simulation, where the cards you have fight -- perhaps somewhat like the D&D Miniatures Game. There could be powerups, lands to allow you to pay for the creatures, or what-have-you, so you could make it like whatever game you wish. For example:
Yujee: I play... THE ETTIN CARD!
Curt: No! The Ettin is strong, tough, and is more than a match for my Human Paladin! Unless I play my enchantment... the HOLY AVENGER CARD!
Yujee: Darn. Okay, draw phase.