Q: change of target and sergei voshkov

Sergei blocks successfully, triggering his built in effect 'look at hand and....'. Acting player wishes to play change of target first, which will end the action. Does the Sergei player get to use his effect before the action is ended as it is triggered first? Or does the COT trigger first due to acting player getting to 'use' 'when blocked' effects first? T

[ quoted text not captured ] The acting player may play CoT first, but that would be to the advantage of the blocking player, who would then get to look at the acting player's hand after the acting player drew the card to replace CoT (and it would be doubly advantageous to the blocker if the drawn card is an action card).