According to Entertainment Weekly, Eminem has already filmed his scenes, although he is not expected to perform on the programme.
Entourage creator Doug Ellin said: "[The scenes are] at a platinum record party for his album [Recovery], which by the time this airs will be platinum, I'm sure. He has a little conflict - a little beef - with Vince [Adrian Grenier]."
Ellin added that Aguilera, who will appear as one of Ari's clients, will sing on the show.
"She's doing a favour for Ari [Jeremy Piven] and performing at a party for him," he explained.
Other guest stars who have signed up for the episode include John Cleese and Minka Kelly along with professional sportsmen Drew Brees, Ryan Howard, Jordan Farmar and Kevin Love.
Entourage continues on Sundays at 10.30pm on HBO. The seventh season finale, which Ellin described as "pretty dramatic", airs on September 12.