Bournemouth forward Defoe, who played in the MLS with Toronto FC, said that Rooney will enjoy life in the US where there is less scrutiny on footballers away from the pitch.
"His family would love it. It is a different lifestyle," Defoe told Sky Sports News.
"There is not so much pressure on and off the pitch. He could probably enjoy his life a little bit without constantly watching what you do and the things you say."
Rooney is expected to sign a two-year deal with DC United this week.