If a challenge is redirected (Crown Regent), power still goes to the initial opponent, right?

I don't think so. The rules reference (p.17) states that redirection happens before any reactions to the challenge initiation. So the power would go to the new opponent.

Edit: Also, the defending player "refers to the opponent of the attacking player against whom (from the attacking player's perspective) the challenge is resolving" (RRp6, emphasis mine).

My doubts come from this: "The challenge is still considered to have been initiated against the original opponent", though I agree the new player is the defending one.

Edit: Ok, thronesdb and scantrell say:
In melee, if a challenge is redirected, the power is still moved to the original defender’s faction card.

Does scantrell work for FFG? I think the FAQ listed on thronesdb is unofficial. I saw the exact same FAQ listed on www.agot.cards, and there it was labeled as unofficial.

These three rules taken together make things pretty clear to me (all emphasis mine):

• This ability is used after a challenge is initiated, before any reactions to that challenge’s initiation can be triggered.
• The challenge is still considered to have been initiated against the original opponent, but it resolves against the new opponent.
• The term “defending player” refers to the opponent of the attacking player against whom (from the attacking player's perspective) the challenge is resolving.

For example, player A initiates a challenge against player B. Player B uses Crown Regent to redirect the challenge to player C. The challenge is now resolving against player C. This makes player C the defending player. Uneasy Truce's Forced Reaction triggers. Power gets moved to the defending player's (player C's) faction card.

If the card had said "the player the challenge was initiated against," then it would be player B.

We've established that the original interpretation in the FAQ was incorrect, the ruling on thronesdb will be changed. The correct interpretation is: power goes to the new defending player. The confusion stems from the ruling on redirect + This Must Be Answered Fiercely that was misapplied to Uneasy Truce.