The McLaren driver set the best lap of the session as the chequered flag waved on a circuit that was all but dry.
He headed the two Ferrari drivers, Carlos Sainz from Charles Leclerc, though nothing can be read from the times themselves given the rapidly changing conditions.
The opening practice hour got underway on time; however, race control announced the pit exit remained closed.
Heavy rain had lashed the circuit earlier in the day, and while the sun had broken through the track itself remained wet.
In some places, that saw large puddles and partial flooding of the Circuit Gilles Villeneuve.
Pit lane finally opened at 13:51 local time – about 20 minutes after the scheduled start of running.
There was little appetite among teams to head out, and the circuit remained silent.
Lewis Hamilton was the first on track, a trickle of others following him out using a mixture of intermediate and full wet tyres.
Valtteri Bottas had opted for the wet rubber but soon reported conditions were good enough for intermediates.
Conditions remained slippery and caught out Zhou Guanyu in the other Sauber, who slid into the wall at Turn 5.
That drew the red flag with 28 minutes remaining, lasting for five minutes.
Track condition did rapidly improve, with a dry line emerging in some parts of the lap.
As that process occurred, times tumbled rapidly making the timesheets largely meaningless.
Things improved such that, in the final five minutes, Ferrari sent Charles Leclerc out on a set of soft compound, slick, tyres.
It remained wet off line, and a handful of small puddles remained – just enough to catch out a callous driver.
Grip on the slicks was extremely low because of the green track but also a lack of temperatures drivers simply weren’t willing to push on to energise the rubber.
In the final minutes, a handful of drivers did bank a somewhat more representative time.
As the chequered flag waved, Norris banked a 1:24.435s to end the session fastest from Sainz and Leclerc.
In reality, the order meant little due to the conditions, evidenced by Norris’ 0.328s advantage at the top of the timesheets.
Oscar Piastri ended the session sixth with Daniel Ricciardo 11th in the abridged session, while Jack Doohan banked three laps without setting a time as he replaced Esteban Ocon at Alpine.
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