Instead of subtracting rotation pieces, the Mets are adding — at least for now.

In something of a surprise move, the club acquired Marcus Stroman in a trade with the Blue Jays on Sunday for pitching prospects Anthony Kay and Simeon Woods Richardson, the team announced. The Mets are also receiving cash in the deal.

The 28-year-old Stroman, a Medford, N.Y., native who represented Toronto in the All-Star Game, is 6-11 with a 2.96 ERA in 21 starts this season. Stroman, who is under club control through 2020, is earning $7.4 million this season.

“Marcus is a dynamic talent who will bring tremendous passion to our team and energy our fans will truly appreciate,” GM Brodie Van Wagenen said in a statement. “As a Long Island native, we believe that Marcus will thrive playing in New York.”

Kay and Woods Richardson were ranked as the Nos. 4 and 6 prospects in the Mets’ minor league system. The left-hander Kay — a Long Island native and former UConn standout — was pitching at Triple-A Syracuse. Woods Richardson, the Mets’ No. 2 pick in the 2018 draft, was pitching at Single-A Columbia.

“The Mets gave up a lot for Stroman,” a major league talent evaluator said. “Hope for their sake they have more moves in mind.”

Noah Syndergaard, Zack Wheeler and Jason Vargas remain as trade candidates from within the rotation. Wheeler, an impending free agent, is the most likely of the group to be dealt before Wednesday’s 4 p.m. deadline, but club officials are still dangling Syndergaard, in particular, with the idea a team might meet their high asking price. The Padres, Braves and Astros are among the teams that have pursued a deal for Syndergaard

Before the Mets’ 8-7 victory over the Pirates, Syndergaard told The Post he doesn’t think he will be traded. And the Mets maintain they will have to be blown away by a trade proposal to deal Syndergaard. But Stroman’s trade tightens an already scarce market for starting pitching, increasing the chances a team will pony up for Syndergaard.

Stroman had been linked to other teams, including the Yankees, in recent weeks. But reports Saturday first began connecting the Mets to the right-hander.

“NEW YORK! Where I was born,” Stroman tweeted Sunday night. “Where my heart lies. Where my family resides. Crazy excited for this part of my journey. Some things were meant to be!”

Stroman, a ground-ball pitcher, will be arriving to a team with a porous infield defense.

The Mets have also engaged in trade talks involving closer Edwin Diaz, according to sources, with the Rays, Dodgers, Braves and Blue Jays among the teams showing the most interest. One source indicated the Blue Jays could potentially acquire Diaz and flip him for prospects from the Braves, but it’s unclear if the Mets’ addition of Stroman eliminated that possibility.

Stroman’s addition is the second big trade of Van Wagenen’s tenure, which began last October. The former CAA agent orchestrated a trade last offseason that brought Diaz and Robinson Cano from Seattle for top prospects Jarred Kelenic and Justin Dunn (along with Jay Bruce, Anthony Swarzak and Gerson Bautista). Cano and Diaz have struggled with the Mets, damaging Van Wagenen’s credibility with the fan base.

Stroman’s addition could make it easier for the Mets to deal Syndergaard for high-level prospects and still compete for the playoffs in 2020. But the Mets also could view Stroman as a rotation replacement for Wheeler or Vargas, should either pitcher — or both — be traded.

If the Mets keep Wheeler, they would have to decide whether to extend him a qualifying offer, which would bring draft-pick compensation. But last year’s qualifying offer — the number has increased every season since it was implemented — was $17.9 million and the Mets might deem that as an overpay for a pitcher who is 7-6 with a 4.71 ERA this season.