The ex-United No.2 believes the Red Devils now know how to handle the movement of Lionel Messi better but says Sir Alex Ferguson's side have to play their own game.
Speaking to Yahoo!, McClaren said: "I do know that it will be a great game of football.
"Barcelona can only play one way, and United can only play one way: that makes for a great game.
"The only thing I can see is that United may have learned lessons from the 2009 final in terms of how to handle the role and movement of Lionel Messi.
"That has to be the main focus: to play their own game, but also to deal with the movement of Messi, which they didn't handle very well on that previous occasion."
The former Middlesbrough boss contrasted the Manchester United treble-winning side he helped manage with the current crop of stars at Old Trafford.
"It's very difficult to say because every team that Sir Alex has built has had different strengths and different weaknesses," McClaren added.
"They all have a common denominator, however, with a driven manager, good leaders, a good philosophy, and good coaching.
"I suppose the game has moved on from 10 years ago when I was there: it is different and more modern now.
"You just cannot compare the different sides, but to achieve the treble was very unique and hard to do."
McClaren also praised Sir Alex's leadership and drive and claims that his direction has played an integral part in the Manchester club's success over the years.
"Leadership is absolutely essential in any team, and that comes from the top. There is no one better than Sir Alex," he said.
"The professionalism, the culture, the competitiveness, and philosophy of the club has been ingrained over the years with him.
"Hard work is also the key to success, along with leadership and professionalism."
Regarding his future on a personal level, McClaren suggests that he would love to work in the Premier League again but has not ruled out a move abroad after previous stints with FC Twente and Wolfsburg.
"I think the experience from abroad has been great: very interesting and beneficial. It has expanded my experience and the success at FC Twente has given me a real sense of achievement," he said.
"Going abroad was not only about gaining experience, but with the intention of really achieving something which I felt that I accomplished.
"When I looked at the future I thought my market was maybe in England, but I feel that anything abroad is still possible.
"But the Premier League is the best league in the world, without a doubt. I know this from my time in Holland and Germany where it is considered the most respected, entertaining and biggest league which people want to see.
"That would be ideal if an opportunity came along, but equally I would certainly not rule out going abroad again."
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