So what would happen if you use Kanans reroll to reroll the white die on Chewie would it be an evade or 2 evades two defense or 1 evade 2 defense?

I suspect that, since they are both your abilities with the same trigger, you would get to choose the order in which they apply. You would pick Kanan's (convert the dodge result into 1 evade, 2 block) and then there would be no dodge results left to convert for Chewie's ability.

Soresu Form 's timing is defending - reroll step, so the conversion seems to happen after he performs the reroll. It doesn't wait until the modifiers step. (The parts would need to be separate abilities to have two timings - or an explicitly delayed effect.)

Wookiee Avenger does its thing in the modifiers step and doesn't see a dodge (from that reroll anyway).

You would thus get an evade and two blocks.

Edit : What if you choose to reroll the black die? Soresu Form does not seem to make any difference between dodges from a die that was rerolled or from another die. It converts "each dodge".