Messi missed Miami's 5-2 loss at Atlanta on Saturday after returning from international duty with Argentina due to what coach Gerardo "Tata" Martino called "muscular fatigue." He was a full participant in practice on Tuesday.
In a statement distributed to media before Miami's training on Tuesday, Martino would not say whether Messi and Jordi Alba, who also missed Saturday's defeat, would feature against the Canadian side, but both players were included in the XI as it continues the chase for a playoff spot from MLS' Eastern Conference.
The loss against Atlanta, which Messi did not make the trip for, was Miami's first since the World Cup winner joined the club in July. Martino's team is second-to-last in the Eastern Conference table, seven points behind 9th place D.C. United, which occupies the last playoff spot, with seven games to play.
"From what I can see he looks good, he looks happy and ready to go," Miami defender DeAndre Yedlin said after Tuesday's training when questioned about Messi's fitness. "Obviously you talk about Leo, he's the best player ever in the game, from the opponent's standpoint it strikes a bit of fear in them as well.
"Experience means a lot, especially in this league. As you saw in that Atlanta game where it's up and down, up and down, [having Messi] helps slow the game down a bit."
After Wednesday's contest with last-placed Toronto, Miami will play a road match against in-state rival Orlando City SC on Sunday and then play Houston in the U.S. Open Cup final on Sept. 27. Martino said after Saturday's loss that his rotations will be focused on the chance at a second trophy of the season.
"The final is just one game, and we're in it," Martino said after the loss to his former team Atlanta United. "It's very tempting to play for a title. Right now we have seven to eight [MLS] games left. And the reality is that it's not a guarantee we'll make the playoffs.
"It doesn't mean we won't go for it, but it's true that we're focused on the 27th."
Miami has picked up one trophy already this season thanks to its Leagues Cup title last month, a win that secured qualification for next year's Concacaf Champions Cup as well as a bye in the opening round.
ESPN's Ross Devonport and ESPN Argentina Federico Bueno contributed to this report.