Since Liverpool is not a weak team, I immediately think that Haaland should be fielded from the start of this match. There's no reason to weaken the squad temporarily because a tough opponent can always seize that opportunity as soon as the first half whistle blows. Doku might be a potential substitute to replace Haaland, perhaps around the 60th or 80th minute, to refresh the attacking line.
Actually I think Alvarez will replace Haaland because there are more players that can play in midfielder, Manchester City only have Rico Lewis and Oscar Bobb as substitute players lol. I have not yet see there's a club which lack of player because most of them are injured, so they only have 9-10 players which is not enough.