A weather-affected opening day in Montreal made for muddled timesheets with Piastri sixth in the opening session, 2.3s off the pace set by team-mate Lando Norris, who was fastest.
The Australian was then only 16th in Free Practice 2 with Norris 20th and last as the changeable weather continued.
“We learned a couple of things,” Piastri said of his opening day’s running.
“Just tricky to know. The track’s been resurfaced to so it was good to see what that’s like.
“It’s still quite bumpy in a few places but I think overall it’s preserved the character of the track well, which is nice.
“Looked alright on the inters.
“We were on the mediums when it was dry, so difficult to know where we sit, but I think everybody’s got the same question.”
Following Free Practice 2, Piastri was warned by the stewards after he took to the run-off at the final chicane during the session in the slippery conditions – one of a host of drivers to leave the road at some point.
“The driver of Car 81 left the track at turn 14, did not touch the orange kerb on the inside and did not follow the instructions outlined in item 15 of the Race Director’s Event Notes.
“However, the Stewards determine that, given the weather conditions, the driver took reasonable action not to rejoin the track in an unsafe manner and did not gain any lasting advantage and therefore consider a Warning as appropriate.”
McLaren has proved a serious threat in recent races, with Norris winning in Miami and Piastri qualifying on the front row for the last two events – converting that to second place in Monaco.
Mixed conditions add a variable to that which could prove a disadvantage as the squad adopts a more conservative approach.
However, Piastri remains confident that, no matter the conditions, he’ll feature towards the front come qualifying.
“I think it also gives us opportunities,” he said when asked if the conditions presented rivals a challenge the established front-runners.
“In the past, we’ve generally been good in those kind of conditions where it’s wet or where it’s quite mixed.
“But now that we’re fighting at the front in normal conditions it potentially gives us a bit more to lose and others not as much.
“I’m confident we’ll still be quick no matter the conditions.”
The weather is forecast to remain changeable for Saturday’s final practice and qualifying, with the chance of rain increasing into the afternoon.
Free Practice 3 begins at 12:30 local time (02:30 AEST Sunday), with qualifying at 16:00.