I suggest playing the lame game. Chun doesn't have the best options for getting through boom spam. Her non-ex Kikokens aren't that great as a shield, no armored moves, her under-projectile slide is short range, and her normal/VT jumps are floaty.
Stay outside Chun's poking range and lay down booms and force the opponent to come to you. If Chun tries to jump over your booms, AA or flash kick her. Mix-up your booms and v-skill projectiles to make it harder for the Chun to get a read jump-in. As the Chun gets closer and is focused on the fireball game, you can mix-things up by suddenly going on the offensive with a jump-in attack combo or dash forward and attack.
