What order do you go in?

Do you have to use Zuckuss first to force the re-roll and then follow up with Crack Shot?

Or can you start with Crack Shot and then use the Zuckuss crew?

Zuckuss happens during your Modify Defence Dice step (before your opponent modifies his defence dice, so he can e.g. spend evade and focus tokens after you use Zuckuss).

Crack Shot happens during the Compare Results step, which is after all dice modifications have happened.

So you have to use Zuckuss first.