Rain had fallen all morning in Montreal to produce a series of small puddles around the circuit, while the cold conditions yielded a track temperature of just 17.5 degrees Celsius at the opening of the session.
Haas pairing Nico Hulkenberg and Kevin Magnussen were first to explore the damp track with the full wet tyre, Hulkenberg setting a 1m34.889s moments before Magnussen kicked off with a 1m34.797s.
The pair improved on their next tour, but Alonso's opening gambit of a 1m32.217s was enough to lift him to the top despite coming across a "blind" Yuki Tsunoda on the exit of the hairpin.
Esteban Ocon collected a 1m31.428s to move to the top, moments after Tsunoda narrowly avoided the Turn 4 exit wall after spinning, and he managed to catch it in time.
Hulkenberg returned to the top with a 1m30.721s as the times kept falling, but was there for a fraction of a second as Tsunoda grabbed a 1m30.685s to leapfrog the German.
Ocon posted a 1m30.348s despite struggling with the final chicane, but Alonso was on the intermediate tyre and set best first and second sectors. The braking zone for the hairpin proved much more difficult to deal with, however, and he had to escape through the run-off.
Max Verstappen then collected a 1m29.190s to go fastest, 0.144s clear of Charles Leclerc - who had braved a full lap on the intermediate tyre.
A 1m28.968s on intermediates then put Valtteri Bottas on top of the pile, but Alonso finally got the chicane before the start-finish straight right and bagged a 1m27.517s to throw down the gauntlet.
Carlos Sainz then moved ahead of his countryman with a 1m27.245s as the intermediate was now the favoured tyre among the field, but was beaten by over half a second as team-mate Leclerc put a 1m26.733s on the top shelf.
After an aborted effort after making a mistake in sector two, Hulkenberg took another run-up and beat Leclerc by 0.3s, and Tsunoda moved into second behind him.
But a 1m25.724s for Leclerc became the new headliner, and Sainz slotted into second with a 0.4s deficit to his fellow Ferrari driver.
Despite complaints about the feeling of his downshifts, Verstappen then threw a 1m24.977s to head the top of the pile, but Leclerc shaded him by 0.127s to reclaim the bragging rights.
Verstappen found almost four tenths on his next timed lap to top the session again, but his efforts to better that were paused as Sainz hit the wall moments after moving up to second, spinning at Turn 1 to clout the barrier and knocked off his nosecone.
The red flag was thus called into service with 30 minutes left on the clock, prompting a seven-minute hiatus in the session as Sainz's car was fished out of the Turn 1/2 run-off.
After the initial laps on the restart were spent bringing the intermediate tyres into their window, Verstappen bettered his time and put together a 1m24.192s to extend his advantage.
On his next tour, he raised the bar with a 1m23.779s as a drying line continued to emerge, and then followed that up on a 1m23.154s as he kept his tyre temperatures up.
The Dutchman's gap sat at 1.6s over the rest of the field, but Leclerc closed that gap to just over 0.2s before Verstappen chipped a smidgen more time out of his best.
But there were no further improvements as the rain began to intensify 10 minutes before the end, ridding the circuit of its drying line and yielding little else in the way of information ahead of qualifying.
Alonso was third fastest with a 1m24.483s, as a late run for Magnussen put the Dane into fourth place ahead of Sainz.
Pierre Gasly spent much of the early phases of the session at the bottom of the timing boards, but the Frenchman managed to corral together time good enough for sixth place, a tenth over home favourite Lance Stroll.
Yuki Tsunoda was eighth having kept the car out of the wall through his spins, while Bottas was ninth after his session came to a slightly earlier end with a loose right-hand wing mirror.
Lewis Hamilton completed the top 10, having felt that the team was "wasting time" running in difficult conditions as it became apparent that he was struggling to fire up the tyres.
Canadian Grand Prix FP3 - Full results
| Cla | Driver | Chassis | Engine | Laps | Time | Gap | Interval | km/h | |
|---|---|---|---|---|---|---|---|---|---|
| 1 |  Max Verstappen |
 |
Red Bull | Red Bull | 22 | 1'23.106 | 188.910 | ||
| 2 |  Charles Leclerc |
 |
Ferrari | Ferrari | 22 | 1'23.397 | 0.291 | 0.291 | 188.251 |
| 3 |  Fernando Alonso |
 |
Aston Martin | Mercedes | 18 | 1'24.483 | 1.377 | 1.086 | 185.831 |
| 4 |  Kevin Magnussen |
 |
Haas | Ferrari | 23 | 1'24.715 | 1.609 | 0.232 | 185.322 |
| 5 | Carlos Sainz |
 |
Ferrari | Ferrari | 14 | 1'24.765 | 1.659 | 0.050 | 185.213 |
| 6 |  Pierre Gasly |
 |
Alpine | Renault | 19 | 1'24.825 | 1.719 | 0.060 | 185.082 |
| 7 |  Lance Stroll |
 |
Aston Martin | Mercedes | 22 | 1'24.944 | 1.838 | 0.119 | 184.822 |
| 8 |  Yuki Tsunoda |
 |
AlphaTauri | Red Bull | 24 | 1'24.955 | 1.849 | 0.011 | 184.799 |
| 9 |  Valtteri Bottas |
 |
Alfa Romeo | Ferrari | 22 | 1'24.988 | 1.882 | 0.033 | 184.727 |
| 10 |  Lewis Hamilton |
 |
Mercedes | Mercedes | 20 | 1'25.087 | 1.981 | 0.099 | 184.512 |
| 11 |  Nico Hulkenberg |
 |
Haas | Ferrari | 20 | 1'25.140 | 2.034 | 0.053 | 184.397 |
| 12 |  Oscar Piastri |
 |
McLaren | Mercedes | 25 | 1'25.191 | 2.085 | 0.051 | 184.287 |
| 13 | Lando Norris |
 |
McLaren | Mercedes | 21 | 1'25.198 | 2.092 | 0.007 | 184.271 |
| 14 |  Alex Albon |
 |
Williams | Mercedes | 21 | 1'25.379 | 2.273 | 0.181 | 183.881 |
| 15 | George Russell |
 |
Mercedes | Mercedes | 20 | 1'25.435 | 2.329 | 0.056 | 183.760 |
| 16 | Nyck de Vries |
 |
AlphaTauri | Red Bull | 24 | 1'25.725 | 2.619 | 0.290 | 183.139 |
| 17 |  Sergio Perez |
 |
Red Bull | Red Bull | 20 | 1'25.857 | 2.751 | 0.132 | 182.857 |
| 18 |  Zhou Guanyu |
 |
Alfa Romeo | Ferrari | 23 | 1'26.750 | 3.644 | 0.893 | 180.975 |
| 19 | Esteban Ocon |
|
Alpine | Renault | 10 | 1'26.840 | 3.734 | 0.090 | 180.787 |
| 20 |  Logan Sargeant |
|
Williams | Mercedes | 16 | 1'27.279 | 4.173 | 0.439 | 179.878 |
| View full results | |||||||||
