The most likely opponent for Canelo Alvarez on September 15 is currently Austin Trout, who holds the WBA "regular" junior middleweight title, in a fight that would be televised on Showtime, possibly against a Julio Cesar Chavez Jr vs Sergio Martinez fight on HBO pay-per-view.
Trout (25-0, 14 KO) is coming off of a dull but fairly dominant win over Delvin Rodriguez on June 2 on Showtime, and has signed with Al Haymon this year, whose fighters have had a lot of TV spots on Showtime in 2012. Trout has a win over Canelo's brother Rigoberto, so there would be some storyline there to help sell the fight. It's a good matchup between highly-ranked 154-pound fighters, but there's no denying that Trout's last fight didn't exactly thrill viewers curious about what he can do in the ring.
Alvarez (40-0-1, 29 KO) beat Shane Mosley easily on May 5 in his last outing, and has had a terrible run of luck trying to find an opponent for his September return.
The first fight thought to be done was against James Kirkland, but that fell through. Paul Williams was signed up and that was good to go, but then Williams was tragically paralyzed in a motorcycle accident. Kirkland re-entered the picture, and then balked again. Initially the shoulder injury that caused him to pull out the first time was blamed, but Golden Boy also said money issues were involved.
After all of that, Victor Ortiz was signed as the opponent for September 15. All he had to do was beat Josesito Lopez on June 23, or even fight to a draw. Instead, he got his jaw broken and lost the fight. Between Ortiz being signed and Ortiz losing to Lopez, Julio Cesar Chavez Jr went out and beat Andy Lee, and then Top Rank announced a September 15 fight between their cash cow and Sergio Martinez.
Golden Boy says there is a potential opponent for Canelo who could keep his next fight on Showtime PPV, but that's probably just lip service. As I've tried to convince people a million times now, PPV companies just aren't going to carry two boxing PPVs on the same night, at the same time. The promoters can do what they want screwing themselves at the gate in Vegas, but the PPV companies have the say on whether or not a PPV is actually available to be watched by their customers.
Richard Schaefer also name-dropped CBS as a potential destination for Canelo's fight, but that appears as unlikely today as it did when he said it, or as it did when Oscar De La Hoya said the last ten times that Golden Boy was totally going to bring boxing back to network TV.
There still remains a pretty good chance that the only fight we're going to see on September 15 is Canelo vs TBA on Showtime, making this business between Golden Boy and Top Rank over this date meaningless. Keep in mind we're assuming -- assuming! -- that Julio Cesar Chavez Jr is actually going to fight Sergio Martinez.