The two British drivers seized a rare opportunity to seize the initiative by running on soft tires shortly before heavy rain poured in with five minutes to go in the second session in Montreal.
The first practice sessions lasted just four minutes due to a problem in the video surveillance system at Circuit Gilles Villeneuve.
Hamilton, a seven-time Formula 1 world champion, led the time sheets with a best lap of one minute and 13.718 seconds, leading Russell by just 0.027 seconds.
Behind were the Spanish Carlos Sainz, from Ferrari, and the two-time world champion Fernando Alonso, from Aston Martin.
The Monegasque Charles Leclerc, from Ferrari, was fifth ahead of the Dutchman Max Verstappen (Red Bull), winner of the last two World Cups and leader of the standings this season after seven races.
The Mexican Sergio Pérez, Verstappen’s teammate and second classified in the season, was eighth ahead of the local hero Lance Stroll (Aston Martin).
Rain interrupts session
The first day of action in Montreal, which began in hot sunshine and ended in heavy rain, was rife with intrigue.
Only 12 of the 20 cars were able to set time in the first session, led by Valtteri Bottas’ Alfa Romeo, due to a failure in the circuit’s video surveillance system, essential for the safety of the competition.
The short duration of the trial meant that the second training sessions were extended by 30 minutes, up to a total of an hour and a half.
The session was marked by two red flags caused by an engine failure for German Nico Hülkenberg (Haas) and problems with Frenchman Esteban Ocon’s Alpine, which stopped on the track at the request of his team.
Subsequently, heavy rain interrupted the last five minutes of the session.
On Saturday, the drivers will take part in a third and final free practice session and in qualifying for the Grand Prix on Sunday.
Results of the first 10 places of the second free trials of the Canadian GP:
Lewis Hamilton (GBR/Mercedes) 1:13.718 (30 laps)
George Russell (GBR/Mercedes) 1:13.745 (31)
Carlos Sainz Jr (ESP/Ferrari) 1:13.844 (39)
Fernando Alonso (ESP/Aston Martin-Mercedes) 1:14.044 (38)
Charles Leclerc (MON/Ferrari) 1:14.094 (38)
Max Verstappen (NED/Red Bull) 1:14.142 (34)
Valtteri Bottas (FIN/Alfa Romeo-Ferrari) 1:14.220 (40)
Sergio Perez (MEX/Red Bull) 1:14.250 (29)
Lance Stroll (CAN/Aston Martin-Mercedes) 1:14.419 (31)
Pierre Gasly (FRA/Alpine-Renault) 1:14.477 (39)