Sundowns are set to host the Catalan giants in South Africa for the second time for a club friendly at the FNB Stadium on May 16, four days after the close of the Absa Premiership season.
The Brazilians last played against the LaLiga champions-elect in 2007, where narrowly lost 2-1 at Loftus Versfeld, where Surprise Moriri scored the goal for the home side.
Mosimane believes the game will be a perfect farewell for Barca legend Andres Iniesta, who is set to leave the Nou Camp at the end of the season, with the Spain international having scored the winning goal in the 2010 World Cup final against the Netherlands at the same venue.
"It doesn't get bigger than Barcelona. I guess it's the biggest," said Mosimane.
"You can also say Real Madrid but we're playing Barcelona now. Okay, that time [in 2007] it was Ronaldinho who was bigger that time.
"But now it is [Luis] Saurez, Iniesta who will be playing this emotional game, his [Iniesta's] last game, if I'm not mistaken, at the FNB Stadium, where scored the winning goal in the World Cup against the Netherlands.
"I think he will be emotional about it and give you guys the opportunity of asking him [questions] and talking about his situation. This how beautiful this can be," the coach added.
'Jingles' also believes the game against Barca will present an opportunity to both local and neighbouring countries to watch the likes of Lionel Messi in action before the World Cup in Russia.
The Sundowns coach was, however, realistic about the battle his side will face against the five-time UEFA Champions League winners.
"I think we know who is going to win. If Barcelona wins, it's normal. Look at the team, look at the names, the budget. We're not even three percent of their budget," he added.
"It's just to share the celebration of Tata, Nelson Mandela and give Africa a chance to witness one of the biggest games.
"I think we will get people from Zimbabwe, Zambia, Lesotho and other neighbouring countries. This would be [the chance] to watch the likes of Messi before the World Cup," he concluded.