Duda homered in the fourth inning. He added a three-run double in the sixth and Cuddyer, who signed with the Mets in the offseason, followed with his home run.
Duda missed the Mets' first 11 exhibition games because of a strained intercostal muscle. He has at least two hits in each of his past three games.
"I'm feeling good at the plate," Duda said. "I feel like my timing is getting back a little bit. Hopefully, it will carry over into the season."
"As far as the injury goes, I was kind set back a little bit," Duda said. "But it feels great right now. My body feels great."
Mets starter Rafael Montero threw six scoreless innings, allowing only two hits. He struck out six and walked none.
Marlins starter Dan Haren gave up seven runs in 5 1-3 innings. Haren allowed six hits, struck out four and walked one.
Marlins: Haren did not allow a baserunner until a two-out single by David Wright in the fourth. He said he started to tire in the sixth, when he allowed five runs.
"I wanted to get around 90 pitches and I was definitely feeling it at the end," Haren said. "I'm sure I'll be a little sore. This spring has been pretty smooth for me until that last inning. I still feel pretty good about it."
Mets: Montero is making it difficult for the Mets to hand Dillon Gee the fifth starter's spot. The right-hander has allowed a total of two runs and seven hits in his last three spring starts.
"Last year, for whatever reason, we did not see the command of his stuff that we had heard," Mets manager Terry Collins said. "We've seen it the last two times against two very good teams. I think we may have to make the best judgment we can make as we get towards of the weekend of who it's going to be."
"I think it's really touch and go," Alderson said. "He says he's going to be ready. We're not doubtful of that, but we want to see his progression."
Alderson said it was unlikely reliever Vic Black (shoulder) would be ready in time for opening day.
GOLD GLOVES FOR LAGARES
Mets center fielder Juan Lagares, who won a Gold Glove in 2014, was presented with a pair of gold boxing gloves by first base coach Tom Goodwin on Monday. Lagares had them hanging in his locker and called them a "trophy."
Last spring, Goodwin presented former-Met Eric Young Jr. with a championship belt for leading the league in stolen bases in 2013.
Mets: Travel to Viera on Tuesday to take on the Washington Nationals. Jon Niese will start for the Mets against Gio Gonzalez.