Following a number of trying race weekends where Aston Martin appeared to have slipped to sixth in the pecking order, the Silverstone-based team bounced back with a stronger qualifying performance in Montreal.
Alonso qualified sixth just 0.228s shy of Mercedes' polesitter George Russell, who beat Red Bull's Max Verstappen in a dead heat in a scintillating Q3 shootout.
The tiny gap between Russell and Alonso, which also covered both McLarens and the RB of Daniel Ricciardo, prompted several drivers to rue their tiny mistakes as the damp, low-grip track surface made it nearly impossible to put together a perfect lap on the Circuit Gilles Villeneuve.
Alonso said his qualifying result was particularly frustrating because he shipped a two-tenth gap to Russell right at the start of the 4.3km loop.
"It was a tricky qualifying for everyone with the wind and the drops of rain. You always lose a little bit of confidence and I think no one did a perfect lap," the two-time F1 world champion said.
"It was the case for me as well. I didn't put everything together in Q3, so when you see that you are only two tenths from pole position, it hurts a little bit."
When asked to explain how he lost the time, he said: "All in Turn 2. It was so oversteering and I lost the car so badly that I was just thinking to abort the lap or keep going.
"I kept going and I was P6, so if two tenths put you in pole position, maybe everything was already in one corner. I was just driving very aggressively after that to recover the lap."
The compromised lap slightly tainted what he felt was a much more positive weekend for Aston, which didn't entirely come out of the blue.
"I think we had a little bit of a full picture now of the car after the first nine races, so we were expecting a little bit better weekend here," he said.
"Already [on Friday] we felt a little bit more confident with the car. The last two events we were out of Q1 so that was race over, basically. But now starting P6 and P9 [for team-mate Lance Stroll] we have chance to score points."
McLaren's Lando Norris and Oscar Piastri were in a similar position as Alonso, qualifying just 0.021s and 0.103s off pole in third and fourth respectively.
"When you're so close, you always think, 'could I have jumped in the car for that little bit more?'," said Norris.
"I know George said he didn't get the most out of it [either]. Just difficult conditions, difficult track layout and challenging, which makes Montreal what it is."
Piastri added: "There are a lot of people out there that can say they could have found three or four tenths out there.
"If you did a perfect lap, you could have been on pole by nearly half a second, so I am sure you will get that from pretty much everyone. Those excuses cancel each other out."
Additional reporting by Jonathan Noble
