The Super League champions taught the three players rugby league as they saw what it takes to be a player with Grand Slam winners Wigan.
Peet said: “They were great. It came about through Betfred, the title sponsor of the Super League. We’ve been there for the Challenge Cup draw.
Wigan won 48-12 against Rugby Football League Championship team Sheffield Eagles at Olympic Legacy Park last Friday in the third round of the Challenge Cup.
It was the Warriors’ first competitive game since they completed the clean sweep, beating Hull KR 9-2 in the Super League Grand Final last year.
Peet said: “They’re great friends of the sport, the club. They suggested bringing Manchester United down as their other partners and bringing some players down.
“We thought it was a great opportunity. We maximised it.”
He praised the three United players - centre-back Maguire, goalkeeper Onana and midfielder Mount - who all visited the Warriors’ training ground at the Robin Park Arena.
Peet added: “The lads got involved. I can’t credit them enough. The lads that came down were open-minded and got on with the lads great.
“They seemed like they were admirers of the sport and the physicality, and they got on with the players well.
“At some point, I’m hoping they will come down to a game. It was a good event. Credit to Betfred.”