The normal hour-long run was cut short by 30 minutes whilst repairs were carried out to one of the metal barriers at turn 11 coming out of the hairpin.
It left the teams and drivers with just half an hour to run through their final programmes ahead of qualifying.
As the regulations state there must be a two-hour gap between final practice and qualifying, it was decided the one-lap showdown would not be delayed, primarily for TV purposes.
To further complicate matters the conditions were again cold and damp due to further overnight rain that finally relented 90 minutes prior to the original start time.
It resulted in an early rush to hit the Circuit Gilles Villeneuve, in particular from Formula One's lesser lights.
As for the heavyweights at Red Bull, Ferrari, Mercedes and Lotus, bar a couple of installation laps, they all waited in their garages and for a dry line to appear, allowing the others to do the donkey work.
With just six minutes remaining they finally ventured out on the fast supersoft tyre, resulting in a frenetic end to the session.
In the final minute alone, as the times tumbled, the lead changed hands half a dozen times, with Webber by far the quickest.
There was such a spread of times, however, given the conditions, that the top 10 were covered by almost 2.5 seconds.
As for Red Bull's Webber, he posted a lap of one minute 17.895secs to finish 0.353secs ahead of Force India's Adrian Sutil, with Mercedes' Lewis Hamilton a further half a second adrift.
Fernando Alonso, who was the first to strap on the supersofts along with team-mate Felipe Massa, was fourth quickest, with the Brazilian down in eighth and almost two seconds down.
In between were championship leader Sebastian Vettel in his Red Bull, Nico Rosberg for Mercedes and Paul Di Resta in his Force India.
McLaren's Jenson Button and Kimi Raikkonen for Lotus completed the top 10, while Marussia's Max Chilton was 14th, 3.7secs back.
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