Souza's contract was selected by the Mariners on Friday.
Souza got off to a hot start at Triple-A Tacoma this season, and he'll start in right field and bat eighth against the Mets on Friday after Jarred Kelenic was sent down. Souza slashed .267/.417/.533 with five homers, 17 runs, 17 RBI and three stolen bases over 22 minor-league games this year, and he'll compete with Dylan Moore for playing time in right field.