Party members have until 5 p.m. eastern on Friday to vote for either Pierre Karl Peladeau, Alexandre Cloutier or Martine Ouellet.
Peladeau, the controlling shareholder of Quebecor Inc. (TSX:QBR.B), is considered the front-runner.
Cloutier and Ouellet served in cabinet until the PQ lost the provincial election in April 2014.
If nobody gets 50 per cent of the ballots on Friday, a second round of voting featuring the top two finishers will be held next week.
Three other candidates pulled out of the contest in recent months for either financial or competitive reasons.
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