does Kath's pilot ability work with ion cannon....the text on the ion says after the hit cancel all die results so im thinking that if say you roll a crit and the defender rolls an evade he is stressed?

So, if the Defender cancels a rolled crit when you attack with an Ion cannon, yes he is stressed. If you roll a crit and it is cancelled by the Ion Cannon, that is you hit and one of the results is a crit that wasn't cancelled by agility dice or an evade token, they are not stressed.

Think of it this way.

Kath's ability only triggers if her Crit's canceled by the opponent, via Green Dice, Evade tokens, or options not yet in the game.

If the Ion Cannon's ability is what is canceling Kath's Crits, then it's been canceled by Kath, and not the opponent. No stress.

If the opponent cancels a crit from Kath while determining if the Ion Cannon hits at all, that still results in a stress.