So me and a friend of mine like to play frequently, and recently we've had a dispute about Kanan Jarrus' ability. My friend likes to play with him due to the low point cost, ok hit points, die sides without resource costs, and ability; however, I think the latter should only be usable on one die per turn, and he disagrees: he thinks that you should be able to use it on both of Kanan's character dice. Any opinions on which one is correct?

With his ability, you have to resolve 1 die before taking an action. Once you resolved a die, then play an action, play a card or resolve a dice or activate a character or any other actions. His ability is like tactical mastery, force speed and seize the day, 2 additional actions are awesome

It's one die per action, and only one die. However an Action and a turn are two different things.

So he could:

Resolve one Kanan Die.

Play a card with ambush and resolve it's effect.

Then resolve a Kanan die before resolving the ambush effect.

What he cannot do is resolve two Kanan dice then perform an action.