Julián Álvarez will never play comfortable as attacking midfielder, he is a striker. I'm sure Guardiola won't force him to play as attacking midfielder if Bernardo Silva and Cole Palmer are available in the squad. Unless these players got injured, so Guardiola must have an alternative to change the formation or try to put Alvarez as an attacking midfielder.
A player who plays well in any position should play in that position. We have seen Julián Álvarez perform well as a striker at the World Cup so I think if he is considered as a striker in the team he will perform better than a midfielder. Guardiwala definitely understands football much better than us so he will definitely take the right decision for the needs of the team. Julián Álvarez may be considered in the regular XI by Manchester City due to injuries to key players in the team. If Julián Álvarez is considered for the regular XI, the question on everyone's mind is in which position he will play. Guardiwala may consider Julián Álvarez as an attacking midfielder in the beginning, if he does not perform well as an attacking midfielder, Guardiwala may change his position and play him in the striker position.