And Garber also says Maple Leaf Sports & Entertainment boss Tim Leiweke is the right man to fix Toronto FC, which has failed to make the playoffs in its seven-year history.
Garber says nothing can be done in south Florida until a downtown stadium plan is finalized. But he called Beckham a "great businessman" with a first-rate partner in TV guru Simon Fuller.
"If you put that together with a great (stadium) facility plan and another economic partner, I think we could have a formula for success," he said after his annual state of the league address Tuesday before this weekend's MLS Cup. "But we're not there yet, but we hope to be able to get there soon."
Garber did not offer a timetable for Miami, which has been without a franchise since the Fusion was folded after the 2001 season.
Asked about the foundering Toronto franchise, the commissioner — who earlier had talked up the league's "competitive balance" — said it now has the right people at the helm.
"Tim Leiweke is one of the most talented and experienced sports executives in the history of our industry," Garber said. "if anybody can figure out how to turn that team around, it's Tim. And if this was a horse race, I'd be going first, second and third with my money on Tim."
Garber pointed to Toronto's hire as GM of former league executive Tim Bezbatchenko, whom he called "wicked smart."
"It might take Tim (Leiweke) and Ryan (manager Ryan Nelsen) and Tim B (Bezbatchenko) some time to get on track but Tim Leiweke has never done anything but succeed at everything he's done. There is no question that I would put my money on him to succeed in Toronto.
"And then you lay on the new ownership structure in Toronto with Bell and Rogers and the fact that (MLSE chairman) Larry Tanenbaum is on our executive committee, the de-facto chairman of our executive committee, it's a killer combination of people. They ought to be successful.
"I'd be encouraged if I was a Toronto FC fan."
In his former job, Leiweke helped bring Beckham to MLS and the Los Angeles Galaxy.
Garber said much the same last year about the new ownership structure of MLSE as well as then-COO Tom Anselmi. He also talked of TFC's planned "bold moves to try to address to try their lack of success on the field.''
Anselmi has since moved on, as has former TFC president and GM Kevin Payne, who was fired in September.
Under rookie manager Nelsen, Toronto finished 17th in the league with a 6-17-11 record. The franchise has shed salary cap baggage, however, and features a young nucleus which the team promises will be reinforced in January with two marquee strikers.
The 19-team league plans to expand to 24 teams by the 2020 season, with franchises already promised to New York (joining the existing Red Bulls) and Orlando, Fla., both of which are slated to start play in 2015.
Garber said Tuesday he was "encouraged" by discussions about Atlanta where Falcons owner Arthur Blank is interested in getting involved in soccer.
Other possible expansions cities include Austin, Minneapolis, St. Louis, and San Antonio. Garber said solid ownership and downtown stadiums were key issues in future expansion.
Garber said last month that while the final number had yet to be worked out, he expected Orlando City to pay the same US$70-million franchise expansion fee that recent previous MLS newcomers have paid.
England's Manchester City and its partner, the New York Yankees, paid $100 million to launch New York City FC.
Under Beckham's landmark deal to come to MLS, the former England midfielder has the right to pay $25 million to start an expansion franchise.
Among other topics Tuesday, Garber said:
— The league has looked and continues to look at what he dubbed "a calendar shift" — changing its current March-October regular season schedule to February-December with a June-July summer break, to match other leagues around the world. The difficulty is caused by the extended break in the middle, he said.
— The league is looking to having the final round of regular-season games kick off at the same time, to maximize the drama surrounding the playoff race.
— MLS "still loses money as an enterprise. And we've got to find a way we can get closer to being a breakeven enterprise."
— The league plans to be more transparent about its rules, with Garber acknowledging what many observers have long thought. "As an emerging league, there are times when we are figuring out those rules as we go along."
Sporting Kansas City hosts Real Salt Lake in Saturday's championship game.
NOTES — Portland midfielder Will Johnson, a Canadian international, and Montreal Impact striker Marco Di Vaio have been named to the league's 2013 Best XI.