Holders Bayern have a slight edge after a 1-1 draw in Manchester last week but Guardiola warned of the English team's defensive tactics and their appetite for quick breaks.
"I think United will be again waiting for us at the back. They will be waiting deep, deep in their own half," the Spaniard told reporters on Tuesday.
"English teams defend and then wait for the quick break. David Moyes also has eight, nine players at the back. They are waiting for mistakes, set pieces and breaks.
"That is why we have to be disciplined. We are playing at home and that is important and we know exactly what to do to attack well."
Guardiola said he was convinced United forward Wayne Rooney would be on the pitch despite a toe injury that has cast doubt over his participation.
"He will play, 100 percent," said Guardiola. "Great players always play the great games and I bet a beer that he will play."
Guardiola brushed aside their first league defeat after 53 games on Saturday to Augsburg, saying he was not after records.
But after the draw in Manchester and another draw against Hoffenheim it is the first time since 2011 that Bayern, who clinched the Bundesliga title in record time last month, have gone three straight games without a win.
"I knew that we would lose eventually," said Guardiola, who had fielded a below-strength team against Augsburg to rest key players.
"The team knows how important the Champions League is. Obviously we still have to play the last few Bundesliga games but our targets are now different ones."
Bayern will be without two key midfielders, with Bastian Schweinsteiger suspended following his red card in the first leg and Thiago Alcantara injured, leaving Toni Kroos and Philipp Lahm to occupy those positions.
"Philipp can play everywhere. We are missing many players and he has shown that he can play that position," Guardiola said. "We know what we have to do and we will apply it. It is little details that will decide the outcome."
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