The Ligue 1 champions are aiming to lift the trophy for the fifth successive time at the Stade de France on Saturday night.
Rennes, meanwhile, will be out to make it third time lucky following defeats to neighbours Guingamp in both the 2009 and 2014 finals.
Despite their dominance of the domestic top flight – PSG are 19 points clear of closest challengers Lille – veteran Italian Buffon feels there can be no sense of complacency in the one-off tie.
"Rennes are a very dangerous side – very dangerous because I remember the game in Rennes and the game here in Paris and we won 3-1 and 4-1, but they were very difficult matches," Buffon told PSG TV.
"I think they are a very organised side, especially in attack.
"I have to say that this year I have been surprised by the standard of this championship, because when you don't play here, you maybe think there's Paris and that's it.
"But I can say, in Ligue 1 I have seen Lille, Lyon, Rennes and also Strasbourg in the league who I think would all do very well in Serie A."
Former Juventus goalkeeper Buffon, 41, has only featured in the Coupe de France run once, but could be drafted back in ahead of Alphonse Areola.
Whoever gets the nod, Buffon, a 2006 World Cup winner and five-time Italian Cup holder, is not expecting a forgone conclusion.
"The fact that it's a one-off match, a final, brings the two sides closer together, the gap isn't as wide as it can be over 38 matches," he said.
"It's a final where anything can happen, you can have a player sent off, an injury, you could hit the post and so we have to be very careful."
Rennes midfielder Hatem Ben Arfa could be set to face his former club, having left PSG last summer.
Despite Julien Stephan's men having not won in four games, the 32-year-old has his eye on an upset.
"We know we are capable of great things and we have really good players, something we proved in the Europa League and against big Ligue 1 clubs away from home," Ben Arfa said to Ouest France newspaper.
"We are capable of winning the final. We need to be united and approach the game as conquerors."