I have a feeling all three will play against Arsenal. Man City have a history of players pulling out of internationals, to then miraculously recover for their club shortly after.
Arsenal are doing the same though, Saka pulled out of England camp and Gabriel is supposedly not fit to play for Brazil. Let’s see if they are all really injured at the weekend.
It's a common tactic not only limited to Man City or Arsenal. No clubs are happy to let their key players play friendlies in their national teams and risk fatigue and/or injuries. Especially when both of the mentioned clubs are still participating in the Champions League quarter-finals as well as are still fighting for the league title and will be playing against each other on Sunday.
Tensions between national and club management are as old as football.
For critical matches, the risk of injury is the worst possible scenario when players play in national teams. That's why I agree that the mentioned teams do not want to send the players. Would you want your most important player to go to the national team and come back injured? Of course, this may not happen, but if it does, it will cause big problems.