The top two have been scoring for fun this season but have also proven leaky at the back at times, especially in the past week.
Last season's two games between the sides saw a thrilling 3-3 draw at Stamford Bridge and a 3-1 win for United at Old Trafford that could have easily finished 5-5.
Chelsea's 2-1 Champions League defeat at Shakhtar Donetsk on Tuesday could also have seen many more goals but for Cech's heroics and the goalkeeper said of Sunday's clash: "I think it will be another exciting game, and we have to defend better.
"But, on the other hand, they have been conceding and leaking goals, so it could be very exciting if both teams play like this!
"The score could be quite entertaining."
This weekend's game will also see Chelsea face Robin van Persie at Stamford Bridge for the first time since the Holland star scored a hat-trick for Arsenal there last season.
Cech admitted Van Persie had made United - who already had Blues nemesis Wayne Rooney in their ranks - even more of a threat.
"He adds goals," Cech said.
"If there is someone who can score goals in every game then it is clear that is another attacking option for them.
"And together with Rooney, it can be a very interesting pair. You can see they've been scoring goals."
Cech urged Chelsea to use their dozy defeat at Shakhtar as a wake-up call for Sunday.
He claimed the European champions' first major loss of the season may have come at the right time as they bid to open up a seven-point gap over United.
The Blues goalkeeper was confident the outcome at the Donbass Arena could turn out to be the ideal "lesson" to take into a clash with their perennial title rivals.
Cech, who will captain Chelsea on Sunday if Frank Lampard fails to recover from a recurrence of a calf injury, said: "If you take it in perspective, it is good that this happened now because Manchester United is a similar team, who play on the counter-attack away from home.
"We will play more or less the same kind of side as Shakhtar.
"So, hopefully, this will serve as a lesson for the weekend."