If City fail to win the two-legged tie they will miss out on the Champions League group stage for the first time since the 2010-11 season.
“We are going to try to score goals and try to convince the players how important it is to play in the Champions League and how beautiful it is and we are going to try and win it,” said Guardiola.
The Spaniard, 45, won the competition twice while manager of Barcelona and Steaua Bucharest boss Laurentiu Reghecampf, whose side last reached the group stage three years ago, says he is ready to face “the best coach in the world”.
“We saw City play Sunderland and have all the information to play football well and achieve a positive result,” he said.
“Even if we face a big team, even if we face the best coach in the world with fantastic results, it is a huge chance for us to prove ourselves.
“I am very confident that we will qualify for the group stage again.”