Verstappen finished 0.424s down on Mercedes' pacesetter Lewis Hamilton in Friday's second practice session, which was extended to 90-minutes after technical issues at the circuit curtailed FP1.
The runaway championship leader said Red Bull "had some work to do" after struggling over the Circuit Gilles Villeneuve's many bumps and high kerbs, which upset the balance of his RB19.
“I think we still have some work to do,” Verstappen said. “The car is not fantastic at the moment over the bumps and over the kerbs.
“It's not too bad but we definitely need to fine tune a few things.”
When asked if that meant Red Bull's rivals have moved closer to them on Canada's unique layout, Verstappen said: “Yeah, let's see. I think we didn't have a good day, maybe they had a good day.
“We know our limitations with the car and with the track, how it is now with the kerbs and the bumps. It's definitely not suiting our package for now, but we'll try to find a few improvements.
“Of course, it was not very straightforward with no running in FP1, but it's the same for everyone, at least we got some running in FP2. A bit more of a tricky session but sometimes you have those days.”
Team-mate Sergio Perez, who finished the day eighth-fastest, added: “It's a shame about FP1, we really needed it.
“I think we have a good base, and we have to make sure we play a bit with the car. It was all a bit in a hurry and there's plenty to understand for tonight.
“I think [our rivals] are looking good. We need to improve our ride as well.”
Hamilton led team-mate George Russell to a 1-2 before the rain hit the track near the end of FP2.
Ferrari duo Carlos Sainz and Charles Leclerc split Aston Martin's Fernando Alonso as they also finished ahead of Verstappen.
Verstappen and Perez were trailing their rivals in every sector of the track in FP2, although competitors are unlikely to put much stock in the team's Friday laptimes.
Sainz proved quickest on the straights, Alonso was on top in the low-speed corners and leader Hamilton set the pace everywhere else.
