United meet Philadelphia Union at Lincoln Financial Field on July 21, followed by a match against the Kansas City Wizards at Arrowhead Stadium on July 25.
They then finish the tour against the MLS All-Stars in Houston on July 28.
Fletcher is looking forward to the tour, telling MUTV: "It's a great tour in America. We've not been there in a while.
"Although three weeks is going to be a long time to be away, there'll be some good games. Personally, playing against Celtic [in Toronto] will be interesting as I'll be up against a few of my Scottish team-mates. But I'm looking forward to it all really."