He intercepted six passes, forced three fumbles and was the team’s second-leading tackler his senior year as the Spartans advanced to the 4-A state championship game.

[4] On August 13, 2017, during a 41–8 home victory against the BC Lions, Gainey became the first CFL player since 1986 and ninth all-time to record four interceptions in a single game.

Gainey's 2018 saw a dip in statistics due to fewer quarterbacks targeting him, but he still nabbed 3 interceptions as well as his first career sack, and was named to his second CFL All-Star team.

[9] In his first season in Edmonton, Gainey made an instant impact after contributing with 47 defensive tackles, one interception, and two forced fumbles in 18 games in 2022.

[10] On June 19, 2023, he was placed on the six game injured list after suffering a shoulder injury in the team's Week 2 loss[11] On January 23, 2024, Gainey was released by the Elks.