When Teemo's 'When I Defend' trigger goes on the chain, does the opponent have to react before or after revealing cards, and does targeting happen before or after revealing cards?

Ruling: You target when the 'When I Defend' trigger goes onto the chain. Once it's on the chain, your opponent can react. All of this happens before you start resolving the ability (revealing cards).

Sequence:

• Teemo's 'When I Defend' trigger goes on the chain
• You choose targets as the trigger goes on the chain
• Opponent has opportunity to react
• Ability resolves (cards are revealed)