The Black Cats hold a 2-1 lead after their first-leg win, and Poyet is keen for his players to create goalscoring opportunities at Old Trafford.
"We're going to play the game as normal. The idea is to play the game and then you make decisions," he told the club's official website.
"It's a game we need to manage properly. We need a complete game – we must defend well, be strong and be good on the ball – much better than the other day [against Southampton].
"We must attack to create chances and score goals. If we score then it will be more difficult for Manchester United."
Despite reaching the last four of the League Cup, Sunderland have struggled in the Premier League, and currently sit 19th in the table.