Light rain continued to cause problems for the teams in Montreal, allowing Aston Martin's Fernando Alonso to top the timesheets in second practice at the Circuit Gilles-Villeneuve.
Alonso's time of 1:15.810s was set on slicks before the midway point of the hour-long session with Mercedes' George Russell second quickest by 0.463s followed by local hero Lance Stroll and Monaco winner Charles Leclerc.
There were troubles at Red Bull with an ERS issue for Max Verstappen's car, while many drivers had various tricky moments as the track got wetter and the expanding puddles prompted a number of minor spins and aquaplaning.
Lando Norris had pipped Ferrari duo Carlos Sainz and Charles Leclerc in the shortened first practice session which had been delayed by a storm and then further disrupted by a red flag for Zhou Guanyu aquaplaning off once the track finally opened for business. The weather remained unsettled as the teams prepared for FP2, with the rain picking up again just as cars headed out on track.
Max Verstappen was the first to head out having opted for slicks, but by the time Leclerc broke cover the rain was heavy enough for Ferrari to opt for intermediates, but he was soon back on pit lane after the team was cited for a 'tyre usage' breach because race control hadn't formally declared it a wet track even though it patently was.
Still on the softs, Pierre Gasly managed to set decent times on softs which encouraged Esteban Ocon to join his team mate on track along with Lewis Hamilton, while Zhou Guanyu was out in his repaired Sauber on the inters after his FP1 accident.
The slick runners started to develop a dry line which brought more cars out to play. Fernando Alonso put Aston Martin top on 1:20.599s on the softs by a tenth from RB's Daniel Ricciardo, pushing Gasly down to third ahead of George Russell.
Almost at once the rain picked up again and the wetter conditions meant everyone found the hairpin and chicane a real handful. If that wasn't enough, a groundhog played a game of near-fatal chicken with Sainz who was nearly collected by a flying Hamilton, while a slippery wet kerb nearly sent Alex Albon into the wall of champions at the final corner.
The rain soon eased off again allowing the times to continuing falling. Leclerc went top on 1:16.556s on mediums, a tenth ahead of Alonso's latest, with the two Mercedes keeping close behind. The news wasn't as good at Red Bull with Verstappen only P13 after jumping from the cockpit of the RB20 on the garage with the smell of burning in the air as the mechanics snapped on the insulating marigolds to investigate the Energy Recovery System. It was the end of his day.
Alonso jumped seven tenths clear at the top with Russell soon up to second ahead of Lance Stroll in the second Aston, at which point another pulse of rain led to a build up of puddles, resulting in a halftime break for the drivers who all retreated back to pit lane. "Weighing up the benefits of what can be learnt from laps, against the risks of what those conditions could bring," was the explanation from the Aston team.
Eventually Ocon roused himself for another go, bolting on the set of inters that Jack Doohan had found no use for in the morning. With just under 20 minutes remaining, he was joined by Leclerc, Alonso, Norris and Stroll who were all out on their used inters from the morning. Proof of the tricky conditions was provided by Leclerc executing a neat pirouette at the hairpin without hitting anything solid.
The rain has dwindled to a drizzle and track was beginning to get drier again by the time the clock ran out, but it was too late to switch back to slicks and attempt to improve on the earlier times. It left the teams somewhat lacking in information and data to analyse heading into final practice on Saturday morning, and very little decided for the weekend at this point.
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