The Bavarian giants opened up a four-point lead over Jurgen Klopp's side as Dortmund suffered a surprise defeat to Wolfsburg, while Guardiola's team cruised to a 3-0 win over Augsburg - making it a record-breaking 37 games unbeaten in the league.
"While I was in Barcelona and in New York, I did not see much of Dortmund, but now I've seen them play a lot and they are a side who can dominate games," Guardiola told reporters.
"They have incredible strikers, but also a good organisation. We've got a bit of time now to analyse them.
"We've got a big, big game ahead of us and this will be a big test for us. I just hope the players all come back from international duty fit."
Bayern are unbeaten after 12 games in the Bundesliga this season.