The pair join the Whitecaps from Boston River in the Uruguayan Segunda Division, with Fernández heading to Vancouver on a one-year loan while Mezquida leaves his old club on a full transfer.
Both players are capable of playing in the midfield and up top, which could help the Whitecaps fill the gaping hole in the attack left by departed MLS Golden Boot winner Camilo Sanvezzo.
“Sebastián and Nicolás are exciting young attacking players with a lot of potential,” Whitecaps head coach Carl Robinson said in a statement. “Both players like to play with the ball on the ground and are not afraid to attack defenders one-on-one with pace.”
Fernandez, 24, is a well-traveled player throughout Latin America, having made stops at Mexican sides Chiapas and San Luis, and Universitario in Peru. He started his career with Danubio in his native Uruguay.
The 22-year-old Mezquida last played with Centro Atletico Fenix in the Uruguayan Primera Division, and he has also spent time with SK Brann and Lillestrøm in Norway. Mezquida has represented Uruguay on several occasions at the youth levels.