Baltimore and Miami are engaged in trade discussions involving the 26-year-old outfielder, according to MASN's Roch Kubatko.
The Marlins have been looking to fill the position with someone who preferably can play right field and hit from the left side, according to MLB Network's Jon Heyman.
Santander, a switch hitter who has played 122 of his 176 big-leagues games in right field, suits Miami's needs.
The Venezuelan produced a strong campaign in 2020, recording an .890 OPS (138 OPS+) with 11 home runs, 13 doubles, and 32 RBIs in 37 games. He missed most of September after suffering a season-ending oblique injury.
Santander did not come to terms with the Orioles on a contract before the Jan. 15 arbitration deadline, so he'll head to a hearing with the club. He's expected to earn either $2.1 million or $2.475 million for 2021.