Whoever the player is, if they encounter a strong defense then they will struggle, not just Haaland. Looking at last season, when the club faced Mamchester City, their defense received special instructions to guard Haaland, and it worked a lot. But Guardiola's clever use of other players to be the second target after Haaland and proven when he struggles to find space because of tight guarding other players who create goals. Now here we can see good teamwork.
Guardiola has a lot of attacking players in the team and many of them have leadership qualities that allow them to take responsibility and therefore it is not so easy to restrain each of these players. Silva, De Bruyne, Gundogan (no longer in the team) could create the chance themselves and score a goal, the value of such players is very high and this allows City to have an advantage. Haaland is a very talented striker, Guardiola could see that in him.
I see Guardiola as a lucky coach, the greatness and experience he had during his tenure as a coach is well connected with the team he is currently handling. A squad filled with experienced players and well-established skills allows Guardiola to rotate under any circumstances. Injuries to De Bruyne, Bernardo Silva and the loss of Gundogan who chose to go to Barcelona can be handled well. Guardiola can still rely on other players to fill their positions, Rodri and Kovacic are able to fill these positions as expected.
The advantage that the Manchester City squad has still puts them as one of the favorites in the UCL this season, Haaland is still Guardiola's mainstay up front to finish the bait that comes to him into a goal.