The former Reds full-back visited Kansas, Philadelphia and Toronto to meet local supporters, check out training facilities and spread the Manchester United gospel.
Sir Alex's men will meet MLS sides Kansas City Wizards and Philadelphia Union as part of United's four-game North American tour, with the Reds playing Celtic in Toronto and an MLS All-Star XI in Houston.
Speaking in Philadelphia, Irwin told manutd.com: "When United go on pre-season tour, we look for different things. One is the facilities - obviously they're second to none here. The second is the quality of the opposition. The MLS will be halfway through the season so Philadelphia Union will be very fit at the time."
And although the North American tour won't feature World Cup stars like Patrice Evra, Nani or Wayne Rooney, Denis assured local fans that there would still be plenty of talent on show.
"You've got the three wise men - Gary Neville, Ryan Giggs and Paul Scholes," he said. "Edwin van der Sar as well. Besides that, you've got a good mix of youngsters. Antonio Valencia's coming across, Jonny Evans, John O'Shea, Darren Fletcher. Federico Macheda and Danny Welbeck are two young lads, so you have a great mixture."