"I played a great first set, and stayed focused for the entire match even if the second set was a lot more difficult," said Nadal.
"It wasn't that easy at all, Fernando is a tough player who has won the title here. This was a very satisfying win for me, I'm glad to be in another final and have the chance to win another time at this great event.
"David and I have always had tough matches and I'm expecting another one on Sunday."
Nadal has dominated the Barcelona event, winning six titles in seven previous appearances. On the one occasion he didn't play -- he missed 2010 with knee problems -- Verdasco took the honours.
Nadal's victory was his 38th winning semi-final in a row on clay, with his last loss coming against Carlos Moya in August 2003.
Raonic had turned in a breakthrough week on the clay of the Real Club de Tenis, winning all of his matches in straight sets.
He defeated Spaniard Nicolas Almagro and upset second-seeded, world number four Andy Murray in the quarter-finals.
"It was very tough to beat Raonic," said Ferrer. "We each had chances but it came down to winning on the key points. He has a huge forehand and he's very difficult to break."
The 21-year-old, ranked 25th, threatened early in the opening set against Ferrer but could not convert on four break chances.
Raonic saved six set points before Ferrer finally clinched it in the tiebreaker from the Canadian's netted forehand.
In the second set, the pair stayed on level-pegging, with Raonic saving the lone break points of the set in the 11th game.
In the tie-breaker, Raonic salvaged a match point as a return caught the line. But Ferrer advanced on his second opportunity from a Raonic error.
