The latest debate is being hosted by CTV Toronto. It is slated to begin at 6:30 p.m. ET.
Meanwhile, a new poll from Forum Research suggests Tory is in the lead among mayoral contenders.
Forum Research said it surveyed a random sample of more than 800 Toronto voters on Monday, including some who have already cast a ballot through advance voting.
Forty-three per cent of the voters who participated said they had voted for, intended to vote for or were leaning toward voting for Tory if the election had been held Monday, compared to 29 per cent for Ford and 25 per cent for Chow.
The poll was conducted via an interactive voice response telephone survey. The margin of error for the survey is three percentage points, 19 times out of 20, according to Forum.
Asked about the poll on Wednesday, Tory said he is running his campaign as if he is "five points behind" the leader.
"I've got a full schedule between now and Monday of activities, very busy, of course, over the weekend covering the entire city," he said.
Chow, Ford and Tory are among dozens of candidates seeking to be the city's next mayor.
More than 161,000 Toronto voters chose to cast their ballots early through advance voting. The rest of the 1.6 million eligible electors will have their chance to do so on Monday.