I have a question regarding a possible scenario that can happen with Lannisters and Greyjoys fight.

Tyrion Lannister:
"You may immediately cancel your opponent's chose House card and return it to his hand. He must then choose a different House card to reveal. If he has no other House cards in hand, he cannot use a House card this combat."

Aeron Damphair:
"You may immediately discard two of your available Power tokens to discard Aeron Damphair and choose a different House Card from your hand (if able)."

If these two cards are revealed, which card triggers first?

Rulebook, Page 19:

There are instances when the exact order of House card
resolution is important. Should a timing conflict occur, follow this
order of operations:

1. Any “Ignore” or “Cancel” text abilities are first resolved in
the player order of the Iron Throne track.

2. Other conflicting text abilities are then resolved in the player
order of the Iron Throne track.