With the semi-finals a one-legged affair this season due to coronavirus, there has to be a winner on the night at Old Trafford.
City lead the head-to-head 2-1 from the three previous meetings at this stage of the competition, and the winner has gone on to lift the trophy on each occasion.
Here, the PA news agency takes a look back at those semi-finals clashes.
1969-70: Man City win 4-3 on aggregate
A late Francis Lee penalty gave City a 2-1 win at Maine Road in the first leg. It looked like United would get a draw when Bobby Charlton cancelled out Colin Bell's opening goal, but Lee held his nerve to score an 88th-minute spot-kick.
Mike Summerbee struck with eight minutes remaining to give City a 4-3 aggregate victory and Joe Mercer's side went on to defeat West Brom in the final.
2009-10: Man Utd win 4-3 on aggregate
The aggregate score was the same, but this time the tie went in favour of the red half of Manchester. Once more, City led 2-1 after the first leg at home as Carlos Tevez tormented his former club with a double after Ryan Giggs had given United the lead.
Late drama at Old Trafford saw United progress and deny City a first major Wembley appearance in 29 years – since winning the League Cup in 1970.
Paul Scholes and Michael Carrick put United in control of the second leg but Tevez was on target again to level up the tie, before Wayne Rooney's stoppage-time header gave Sir Alex Ferguson's team a 3-1 win on the night. United beat Aston Villa in the final.
2019-20: Man City win 3-2 on aggregate
Pep Guardiola's side ripped United apart last season in the first leg at Old Trafford, with goals from Bernardo Silva, Riyad Mahrez and an Andreas Pereira own goal giving City a 3-0 half-time lead. Marcus Rashford pulled one back in the second half.
United gave themselves hope of a famous comeback when Nemanja Matic put them ahead in the second leg at the Etihad Stadium, before the midfielder's 76th-minute red card all-but ended those hopes.
City held on and reached the final with a 3-2 aggregate win, going on to lift the trophy for the third year in a row with a victory over Villa in the final.