More than 92.5% of the votes cast at the special meeting were in favor of the proposed deal, the company said in a statement.
The C$31 per share deal, announced in May, received a green light from Canada’s transport minister last month.
The transaction is expected to close later this year or early next year if it receives remaining regulatory approvals.
WestJet has reported a decline in net profit for each of the last three years, hurt by rising fuel costs, pressure on ticket prices and other problems.
The WestJet purchase will be led by Onex Partners, Onex’s private equity platform focused on larger investments.
Reporting by Debroop Roy and Shanti S Nair in Bengaluru; Editing by Bernard Orr