City will arrive at Wembley this weekend hoping to complete the second part of the incredible bid to win the Premier League, Champions League and FA Cup in a single season.
Guardiola's team clinched a fifth Premier League title in six seasons with three games to spare, giving the City boss an opportunity to rest key players and fine-tune his tactics ahead of the two matches that will define their season.
After facing United in the first all-Manchester FA Cup final, City travels to Istanbul to play Inter Milan in the Champions League final on June 10.
Guardiola's sole focus this week has been United, which stand in the way of the club's attempt to emulate its neighbors' historic treble triumph in 1999.
United is the only other English club to have won all three major trophies in one campaign and Erik ten Hag's men would dearly love to stop City moving closer to matching the achievement.
United's treble winners only secured the title with a win against Tottenham on the last day of the season and needed an astonishing late fightback to beat Bayern Munich in the Champions League final.
Those victories tested the nerves of everyone associated with Alex Ferguson's team and City could be about to experience the most fraught part of its own treble chase.
Inter, which is third in a relatively weak Serie A, will be underdog against City next week.
But United should pose a sterner threat and Guardiola is well aware Ten Hag's team has enough quality to hurt City if it is not at its best.
Guardiola personally watched United's recent 4-1 rout of Chelsea, while memories of City's 2-1 defeat at Old Trafford in January still haunt the Spaniard.
"I am more focused on United right now. I saw their game against Chelsea. I was really impressed and I have started to review a little bit what they did to us in the game at Old Trafford," Guardiola said. "As in the past, we have to be careful. I would be careful anyway but after Thursday and their games recently, we are going to prepare the best we can."
'Special game/' Despite Guardiola's caution, Abu Dhabi-backed City has become English soccer's first dynasty since United's Ferguson era and has every reason to believe it will lift the FA Cup for the second time in the Spaniard's reign.
City, which thrashed United 6-3 in October, reeled off a blistering streak of 12 successive league victories to land a third consecutive title. Last weekend's 1-0 loss at Brentford, in which City fielded a weakened team, was the first defeat in 26 games in all competitions.
Inevitably, Erling Haaland will be City's key man at the end of a brilliant first season in England. The Norway striker has scored 52 goals in all competitions, including a single-season record 36 in the Premier League.
United is among Haaland's victims after he hit a hat-trick against them in October, but Ten Hag came up with a plan to hold him goalless in the rematch.
That was another notable achievement in an impressive first season for Ten Hag, who ended United's six-year trophy drought with a League Cup final victory against Newcastle in February.
Ten Hag is only the second manager in United's history to win a major trophy in his first season and adding City's scalp at Wembley would underline the vast improvement under the Dutchman.
United, which finished third in the Premier League, is relishing the opportunity to ruin City's treble hopes, even without injured forward Anthony Martial.
"Of course, we know it's a big final, a special game. We've been the whole year fighting to be in that position to win titles. We will try absolutely everything to try to win," United keeper David De Gea said.
© Agence France-Presse