Nadal, who has won the tournament the past two years, beating the Swiss in last year's final before clinching his second French Open crown with victory over Federer in Paris, will start as the favourite.
"After he proved how incredibly tough he is on clay, it's no surprise that he's going to play well again," Federer told reporters on Saturday.
"I think it will be interesting to play again. We had some great matches last year."
Nadal will, as usual, take nothing for granted against his closest rival.
Federer has been in a class of his own in his last two matches in the principality, defeating two claycourt specialists en route to the final.
On Friday, he thrashed Spaniard David Ferrer 6-4 6-0 before easing past 2003 French Open champion Juan Carlos Ferrero 6-3 6-4 in Saturday's semi-final.
Nadal has not been tested either, with victories against Argentine Juan Ignacio Chela, Belgian Kristof Vliegen and German qualifier Philipp Kohlschreiber.
On Saturday, he seemed on track for the quickest win of the tournament against Tomas Berdych but after clinching the first set in 23 minutes.
But he then had trouble holding off the Czech's challenge before clinching a 6-0 7-5 victory.
