Ronaldo moved on to Real Madrid for a world record fee following Barca's 2-0 win over United in the 2009 Champions League Final in Rome and the Catalan club face the English Premier League champions again in Saturday's final in London.
"This Manchester team is much more unpredictable without Cristiano Ronaldo," Alves told reporters at a media open day at Barca's Nou Camp stadium.
"You can see now that they have built a much more balanced side, stronger than a couple of years ago," added the Brazilian, who missed the 2009 final through suspension. "They are dangerous across the board and packed with great players."
Barca and United are both seeking a fourth European Cup at Wembley stadium on Saturday, which would put them level with Ajax Amsterdam and Bayern Munich and behind only Liverpool (five), AC Milan (seven) and Real Madrid (nine).
Playmaker Xavi, whose control of possession and distribution is a key element of Barca's strategy, said United were not as direct in attack as they used to be with Ronaldo in the side and prefered to keep the ball and build through the midfield.
"I don't know whether it's because of Cristiano Ronaldo but it's true that Manchester is a team that works as a unit, very solid on the pitch," he told reporters.
"This team likes to have the ball more and is not as direct as it used to be."
Xavi's team-mate David Villa, who began his first season at Barca on fine form but has found goals hard to come by in recent months, said Ronaldo's departure had liberated United.
"Right now, sincerely, I believe that in the final you will see the two best teams in Europe," he said.
"They (United) have grown as a side since 2009," added midfielder Andres Iniesta.
"They have made a very good impression in the Premier League, dominating and proving that they have the desire to remain among the best and fight for the Champions League," he said.
"The team is very complete and I don't think that the adjustments of the past two seasons have changed much. They are stronger because they know each other better."
