Trevor has a rage ability that makes him invulnerable for about fifteen seconds, the only way Michael could ever win the fight would be in an instance where Trevor wouldn't fight back.
Trevor would still be invincible during Michael's bullet time, so it would be like shooting Godzilla with a BB gun. Plus Michael is not invulnerable during bullet time so all Trevor has to do it hit him.
Next time you play the game , start a shoot out with the cops, Michael can aim faster than the police. However he is unable to actually dodge the bullets coming at him, this is because he only perceives the situation in slow motion, he is not super fast.