The boss points out that where the Manchester clubs finished in the Premier League table, previous form or even past meetings have no bearing on a one off game at a neutral venue.
He also added that expectations placed on his players by the media and pundits are always incredibly - and perhaps unfairly - high.
“We are used to it,” said Guardiola.
“Starting from September, October [they say] we would win Champions League and Premier League by 25 points - every year.
“We say, ‘okay you’re right’ and they say it’s boring. When you win one point or two points over Liverpool many times and Arsenal it’s not boring.
“If you tell me we would win the title by 15, 20 points every season, I would say, yes, it’s boring. But it’s not going to happen.
“People think what’s going to happen because we ended 31 points ahead of United and so it will be easy – I understand that.
“But this is a different competition. It is one game [and everything can happen].
“It can be 10 v 11, bad decisions, mistakes and you can lose a game. We know we can lose a game.
“In a long period we have been better than United this year. It’s obvious. It’s facts. Every game, we are there.
“But in one game anything can happen. The players know and feel it.
“So, I hope we are ready to play the last game of the season - the FA Cup is, wow! It’s nice. The FA Cup is the FA Cup. It deserves all our focus.
“Last year, I think we started well after Gundo’s goal. After a good period, they equalised and then the second half, we played well, we scored the second and we played really good.
“In the last minutes, they put a lot of players up – I remember perfectly – they played long balls and we struggled a bit, plus from free-kicks and corners in the last minutes.
“But in the end, we handled it well and deserved to win that game. In all honesty, that’s past and it doesn’t matter the opinion of that. It was a final - both teams had moments, but in general, we had a good final.
“Always I had the feeling to play the final of the FA Cup is an exception.
“It was difficult to win against Spurs away, win against Newcastle and Luton [and Chelsea].
“Arriving here is difficult. I don’t take this for granted. Respect our opponent, take it seriously, we can lose every single game and at the same time we can win them.
“I never had the feeling it doesn’t matter. Absolutely not. The final, when you arrive is such a privilege, to be here again.
“Always I have said to my players, what you have done to arrive in the final is difficult and I don’t change my mind.”
Asked about players who have taken part in the cup run and their development along the way, he replied: “Everyone has their own skills and qualities and we need some specific things and we will need them.
“We arrive all together. Everyone makes their own contribution. We are all together. We can play different ways and they all are fit and want to play. I need to decide. Train, talk with staff and we will decide tomorrow.”
