Running in his starting position of fourth, Russell was sent crashing into a wall at Turn 9 after his W14 hit a kerb on the exit from which he was unable to gain full control.
The bang with the right-rear wheel sent debris across the Circuit Gilles Villeneuve, sparking a safety car period, the 13th in the last 21 races at the Montréal venue.
Although the Briton clawed his way back into the points as those ahead of him made pit stops, he was running in 12th when he was told to retire the car due to brake issues with 15 of the 70 laps remaining.
Explaining the incident, Russell said: “I just went a bit deep into the right-hander (Turn 8) and through the left (Turn 9) I just touched the kerb which I clearly hit with the bottom of the car.
“The next thing I knew I was sort of up in the air and when I landed I lost the rear and I was in the wall.
“Kicking myself because it's such a small error with big consequences. That's how it is on circuits like this. Not good enough from my side.
“I did a good job to get back into the mix but obviously I had a bit of an issue with the brakes. It all stemmed from my mistake.
“Sorry to the team. They've put so much hard work in, the car's performing well. We weren't expecting to be competitive here, yet we put up a good fight.
“It looks good for the future, just disappointed in the now.”
Mercedes was fully expecting to be off the pace at a high-braking circuit with slow corners, yet team-mate Lewis Hamilton and Russell qualified third and fourth, with the seven-time F1 champion retaining that position at the chequered flag.
Hamilton finished 14 seconds adrift of Red Bull's Max Verstappen, an improvement of 10 seconds compared to when he was runner-up to the two-time title-holder at the previous race in Spain.
Addressing the positives from Mercedes' perspective, Russell added: “The pace was strong, we're there on merit.
“We've still got work to do but this was a track that on paper was really challenging for us, and we clearly put up a really good fight, taking it to Aston (Martin) and Ferrari.
“Let's see what the upcoming races bring. The team is doing a really great job at the moment and it is exciting for the future.
“Obviously, I'm just disappointed with the hear and now.”