GRAVENHURST, Ontario — When Prime Minister Justin Trudeau’s image as a liberal reformer crumbled during the lead-up to Canada’s national election, an opportunity opened for competing left-wing parties to attract disaffected voters.

But as the campaign heads into its final week, it hasn’t quite played out that way.

The prime minister and his Liberal Party are locked in a neck-and-neck race with the Conservative Party, according to most polls, with fewer voters looking to the other choices on both the left and right. Many may not vote at all.

[Canadians have elected a Liberal minority government, granting Justin Trudeau a second term as prime minister.]

In 2015, when Mr. Trudeau was first elected, there was plenty of enthusiasm for his party, said Jon H. Pammett, a professor of political science at Carleton University. “This time there is not a lot of enthusiasm for any of the parties or any of the leaders,” he said.