2021 National Bank Open – Men's singles
Daniil Medvedev won the title, defeating Reilly Opelka in the final, 6–4, 6–3. It was his fourth ATP Masters 1000 title and 12th career title. Rafael Nadal was the two-time defending champion from when the event was last held in 2019 and was vying to tie Ivan Lendl's record of 6 Canada Masters titles, however he withdrew from the tournament due to a foot injury. Seeds. All seeds received a bye into the second round.