Cecil, formerly with the Blue Jays, can face both lefty and right-handed hitters. His contract is the highest free-agent deal ever for a Cardinals reliever.
Dunn also isn't a true lefty specialist. Not to say Dunn will get the same exact terms, but the market is trending for him to make more than $5 million annually.
The Marlins don't have much left-handed depth in the bullpen. Hunter Cervenka, Justin Nicolino and Elvis Araujo are the only southpaws on the 40-man roster with big league relief experience. Nicolino has been a starter throughout his career, but saw some action out of the bullpen in September.
The Marlins acquired Dunn from the Braves after the 2010 season as part of the deal for Dan Uggla. He has been the primary left-hander in Miami's bullpen since.
Dunn's been durable and dependable, and his 405 appearances are the most ever by a Marlins pitcher. In his Miami career, Dunn has a 3.59 ERA in 328 innings with 357 strikeouts and 150 walks.
Dunn had never been on the disabled list until the start of 2016, when he was sidelined with a left forearm strain which caused him to miss two months. The lefty returned on June 1, and he appeared in 51 games with a 3.40 ERA in 42 1/3 innings.
The Marlins acknowledged Dunn may have been rushed back, which may explain why he started off slowly. In June, he posted a 5.40 ERA in 8 1/3 innings. But he got sharper as the season progressed, and he had a 1.42 ERA in July and 2.19 ERA in August.
Dunn's velocity also remained high. According to Statcast™, his four-seam fastball averaged 94.16 mph, with the MLB average at 93.04.
One way the Marlins are considering strengthening their overall pitching is to compile as deep of a bullpen as possible. The heavy use of relievers in the playoffs has many clubs rethinking how to construct their rosters.
"You look at the playoffs, and how that changed so much," Marlins president of baseball operations Michael Hill said recently at the General Managers Meetings. "Obviously, you can't do that over 162 games, but if you can have it as deep as possible, you're giving yourself a chance with that quality bullpen."
Joe Frisaro has covered the Marlins for MLB.com since 2002. He writes a blog, called The Fish Pond. Follow him on Twitter @JoeFrisaro and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.