Castellanos hit his fourth career grand slam, Jordan Zimmermann pitched seven strong innings and the Tigers beat the Toronto Blue Jays 9-1 on Sunday.
Manager Ron Gardenhire scheduled the pregame meeting, a relaxed session in which players were invited to say whatever was on their mind. Castellanos called it an opportunity to "just kind of address the elephant in the room."
"It gave anybody a chance that wanted to speak up to speak up," said Castellanos, adding that Victor Martinez, James McCann and Gardenhire were among those who talked.
JaCoby Jones hit a two-run homer as the Tigers won for the first time since June 17, when they completed a three-game road sweep of the Chicago White Sox.
Castellanos nearly hit another home run in the ninth but Blue Jays outfielder Kevin Pillar made a leaping catch at the wall.
"I felt like I was going to have a chance to make a play," Pillar said. "A ball like that hit as high as it is it allows me time to kind of track the ball and track the fence and go up to try to make a play. "
Castellanos stopped on the basepaths to applaud Pillar's catch before turning and heading back to the dugout.
"What else can you say the end of the day besides 'What a play,'" Castellanos said. "It sucks it had to happen to me but plays like that have to happen to somebody."
Niko Goodrum had a career-high four hits and Jose Iglesias had two hits and two RBIs for Detroit, which had lost 12 of 14 at Rogers Centre.
"That was a fun win, a really fun with with a lot of great swings," Gardenire said.
Zimmermann (3-0) allowed one run and five hits in his third start since returning from a shoulder injury that caused him to miss more than a month.
"He had a great curveball today," Gardenhire said. "That's probably the best curveball I've seen all year out of him."
Wearing red jerseys and caps for Canada Day, the Blue Jays couldn't deliver a win for the holiday crowd of 37,445.
Tigers outfielder Leonys Martin left with a sore left hamstring after his bases-loaded bunt single in the fifth brought home Detroit's first run. Martin was replaced by Victor Reyes.
Following the game, Gardenhire said Martin would be placed on the 10-day disabled list. A corresponding roster move will be made before Monday afternoon's series finale.
Castellanos followed with his 13th home run, a shot that bounced off the top of the wall in right. It was his first grand slam since Sept. 8, 2017, also against Toronto.
Castellanos also made a fine catch in right, reaching back to grab Russell Martin's line drive for the final out of the fourth.
Iglesias chased Blue Jays left-hander J.A. Happ (10-4) with a two-out, two-run single in the sixth.
Happ matched season-worsts by allowing seven runs and 10 hits in 5 2-3 innings.
"It's not a pretty outing and I own that," Happ said.
Happ had won six consecutive decisions since his previous defeat, May 10 against Seattle.
Teoscar Hernandez tripled in the first and scored on a two-out double by Justin Smoak, but Zimmermann recovered to retire the next nine Blue Jays batters.
For the second straight game, the roof was closed at Rogers Centre because of high heat and humidity.
Blue Jays RHP John Axford complied a list of more than 500 songs by Canadian artists and has been playing his mix in the clubhouse all weekend. Axford's 'Oh Canada!' playlist can be streamed using the online music service Spotify.
NOT YOUR DAY
The Blue Jays are 14-26 on Canada Day, including a 12-17 mark at home.
Tigers: RHP Alex Wilson, who left in the eighth inning Saturday because of a sore left calf, was not available. ... RHP Drew VerHagen (nasal fracture) pitched one scoreless inning for Triple-A Toledo Saturday night, his first rehab appearance. VerHagen has been out since June 20.
Blue Jays: Toronto optioned utilityman Darnell Sweeney to Triple-A Buffalo after the game and will make a corresponding roster move Monday.
Tigers RHP Mike Fiers (5-4, 4.04) faces Blue Jays LHP Ryan Borucki (0-1, 3.00) in Monday afternoon's series finale. Fiers is 0-2 with a 5.91 ERA in two career starts at Rogers Centre. Borucki made his major league debut at Houston last Tuesday, allowing two runs in six innings.