The Norway striker has made a stunning impact at City, scoring 12 goals in just eight appearances since his £51million move from the German side.
Two other recent signings, Sergio Gomez and Manuel Akanji, are also former Dortmund players.
"They know these players better than I know Dortmund players, that's for sure," said Guardiola, whose side beat Sevilla 4-0 in their opening Group G game last week with two goals from Haaland.
"They can get that benefit but we'll see (on Wednesday) if it's an advantage or disadvantage, but these three know the qualities of the Dortmund players too."
City midfielder Ilkay Gundogan, another former Dortmund player, has been impressed by Haaland since his arrival.
"The numbers speak for themselves," the Germany international said. "He's doing great on the pitch but his character, attitude and determination off the pitch is something incredible."
City are hoping Haaland can prove the final piece of the jigsaw after years of near misses in the Champions League.
"We will see," Gundogan said. "It will be a very tough competition and little details can decide the outcome."