The deal will see the 20-year-old midfielder take part in a training camp before being offered to the league's clubs in the draft on Jan 13.
Rooney, who played at Macclesfield after following his brother through the Everton youth ranks, has already spent time on trial with the Seattle Sounders and Portland Timbers, stints that convinced MLS he could have a future in the league.
Rooney said that he had offers from elsewhere, but he was attracted by the chance to make a name for himself overseas, out of his brother's shadow.
"There were a few teams sniffing around from the higher leagues but I wanted to change my career and go to the United States to build on my own career over there [in the USA]," he told Major League Soccer's official website mlsnet.com.
"That's why I want to get over there [to the USA] - so it's just me. And I want to build my own career over there and do my best. Hopefully I'll enjoy it."
The pre-draft training camp begins on Friday in Baltimore.
