Rain falling throughout the day in Montreal meant qualifying took place in similar wet conditions to FP3 earlier on Saturday afternoon, which was led by Alonso.
The Alpine rider stunned Sainz as he finished second on the final timed lap of Q3 where all riders were fueled up to run for the full session to take advantage of the track drying out and get the tires into optimal working order bring to.
Verstappen was untouchable, led from the off in Q3 and worked the pole benchmark down to 1:21.299 minutes.
Sainz had looked like he might narrowly pass Verstappen after setting the fastest first sector on his last lap, but while he stayed in contention despite losing a fraction in the middle sector, a big slide on the exit of the last corner meant, that he lost enough time for Alonso a few moments later before his compatriot get on.
Lewis Hamilton was fourth for Mercedes, which split its strategy towards the end of Q3 by fitting softs on George Russell’s car, a decision that backfired when the Brit spun on the slicks in the early corners on his first lap.
Russell fell from the leading positions to eighth by the end of the third quarter, with the Haas duo Kevin Magnussen and Mick Schumacher pushing the Brit down in fifth and sixth.
Then came Esteban Ocon, while Daniel Ricciardo and Zhou Guanyu completed the top 10.
Zhou is one of several drivers who will face a post-session investigation for driving during a number of off-track moments during qualifying or trying to find space in traffic in the earlier segments.
Q2 started with the drivers splitting whether to stay on the wet tires used throughout Q1 or switch to the intermediates, with Alonso leading that mix early in the segment just before Sergio Perez caused a red flag, which drove into the barriers the Turns 3/4 chicane.
The Red Bull driver was also on the intermediate lap but locked up with his right front axle and after pulling the other front brake, he slid across the grass and quickly crashed head-on into the guard rails.
Although his car did not appear to be massively damaged, Perez took a long time to put it into reverse and when he did, he was unable to reverse due to his nose being buried in the barriers and was ordered to shut his engine down with the barriers he had to be rearranged after his car was craned away without the front wing.
When the session resumed after a 12-minute delay, all of the remaining riders backed onto the Inters, with a dry line looming.
Leclerc didn’t bother to join them as by reaching Q2 he ensured he started ahead of Yuki Tsunoda at the back of the grid thanks to their engine change penalties, but Lando Norris also failed to appear at the start of the remaining nine minutes from Q2.
Norris reported an engine problem ahead of the red flag, which restricted him in the McLaren garage until just two minutes remained as the team tried to find and fix the problem, and although he got out for a lap, he was soon served ordered Box again after touring a few seconds off the pace.
By failing to time after the red flag, Norris’ banker lap left him in 14th place early in Q2 and behind Perez’s best time ahead of his exit, with Leclerc not participating in the middle segment and so busting out in 15th up front his grid drop before the race.
With three cars in trouble or off track, only two drivers were in danger of retiring and as Hamilton jumped up the order on his final lap, the pressure was on Alex Albon, Valtteri Bottas and Ocon.
The first two names set personal bests with Bottas up front, but Ocon’s improvement on the final lap in Q2, topped by Verstappen, knocked out the Finn.
As in Q3 and Q2, all drivers generally rode throughout the opening segment as times improved by about six seconds as they blew water away from the racing line, barring large puddles of standing water at the apexes of the first two corners and the Exit of the hairpin late in the lap with Verstappen finishing in the lead.
Pierre Gasly retired in 16th, with AlphaTauri reporting that he was suffering from a brake problem on his left front wheel, possibly contributing to his exit in late Q1 via the Turn 9/10 chicane.
Gasly went off the track only briefly, but by not staying to the left of the bollard in the drain before the short straight to the hairpin, he was not following instructions from race officials and will face a post-session investigation.
Sebastian Vettel was frustrated to be eliminated in 17th after finishing third in the similarly wet FP3 session earlier on Saturday afternoon, with Lance Stroll’s 18th place compounding a miserable qualifying for Aston Martin.
The other local hero, Williams driver Nicholas Latifi, was eliminated in 19th, finishing ahead of Tsunoda, who pitted a few minutes from the end of Q1 knowing he would be starting on the last row anyway.