The battle lines in Toronto's upcoming mayoral race may feel familiar to some: A conservative has left office and a wide open race to replace him has taken shape. Candidates lament a city in disrepair and spar over the future of the waterfront.

It all resembles 2003, city hall watchers say, when Toronto elected its first – and only – centre-left mayor since amalgamation in 1998.

Not since David Miller left office in 2010 has a progressive candidate stood a better chance of winning the mayor's seat, said Zack Taylor, political science professor at Western University. Progressives running this time can learn from Miller's first successful campaign, Taylor added.

Miller told The Canadian Press that he hears the echoes too.

"There was a feeling that the city wasn't investing in the priorities of the people," Miller said of his 2003 run. "And I think there's a parallel today. We do see a lot of services declining."

Miller's tenure interrupted 18 years of conservative mayoralties starting with his predecessor Mel Lastman, through to Rob Ford and John Tory.

Tory secured a third term, winning a landslide victory in the October 2022 election, before resigning in February after admitting to an affair with a staffer.

There is evidence that Tory remains popular, with some polls ahead of the June 26 mayoral byelection putting him in first place – even though he's not running in the field that included a whopping 102 candidates when nominations closed on Friday.

In the packed race, veteran politician Olivia Chow, a former federal lawmaker and a long-standing member of the left-wing New Democratic Party, is a leading candidate. Coun. Josh Matlow is also being championed by the progressive left.

The list of others seen as vying for centre-left votes includes former deputy mayor Ana Bailão, former provincial education minister Mitzie Hunter and Coun. Anthony Perruzza.

Even though voters overwhelmingly backed the conservative Tory less than a year ago, Miller and Taylor argued that Toronto may be ready to turn the ideological page.

For Miller, a successful progressive candidate needs to be "straightforward, clear and consistent," including by talking candidly about the need to hike taxes to boost services, as he did in 2003.

Miller said progressives can also gain traction by running against what he described as a "raft of backroom dealing, particularly between the mayor and the premier." When Miller first ran, his predecessor Lastman's final term had been marred by a municipal finance scandal and a confession to an extramarital affair.

During Tory's administration, many criticized the so-called strong mayor powers granted by Premier Doug Ford, which allow the mayor to pass a budget with one-third council support.

And then there's the waterfront. While Miller's campaign made headlines for his opposition to island airport expansion, several centre-left candidates have turned Ford's plans for a privately-owned spa at Ontario Place into a larger battle over a publicly accessible waterfront.

The issues that fuelled Miller's rise may have resurfaced but, "whether it (resonates) as much, you know, time will tell," the ex-mayor said.

Taylor, the political science professor whose expertise includes local election campaigns, stressed another crucial element of Miller's winning campaign: his ability to retain the support of voters in downtown wards, who lean left, while making inroads with suburban voters who skew conservative.

"The lesson for progressives is that they need to figure out how to broaden their appeal without sacrificing their principles that they hold dear," Taylor said.

To some, comparisons between 2003 and 2023 don't hold up.

Deepening inequality, political polarization and the provincial government's intrusion in city politics are standout issues for this campaign, said first-term city Coun. Alejandra Bravo, who forms part of council's progressive wing.

"We're coming out of a pandemic, which is going to define a generation. With that, it brings a whole host of problems, including a mental health crisis," said Bravo.

Bravo helped found Progress Toronto, a progressive advocacy group that backed her 2022 council run and has endorsed Chow.

A progressive candidate needs to commit to majority rule at city hall and reject strong mayor powers, Bravo said.

She also wants to see who takes money from individuals, versus developers, and who is willing to discuss tax hikes and the need for new sources of municipal revenue.

The crowded field has also prompted speculation about whether support will coalesce around a progressive standard-bearer, another echo from the 2003 campaign. Barbara Hall, a former New Democrat and a pre-amalgamation mayor, started as the clear 2003 front-runner, but as her campaign faltered, Miller strengthened in what turned into a two-way race with Tory.

But this mayoral byelection campaign is "uncharted territory," said longtime Coun. Gord Perks, a chief Tory critic and friend to Miller.

In an abbreviated byelection campaign, without conspicuous party banners, and with hundreds of thousands of eligible voters casting ballots only for mayor, this election is unlike any other in Canada, he said.

"Anyone who's forecasting that there's going to be vote splitting, or that somebody's going to have to bow out, or that one candidate from each political flavour will emerge, just doesn't understand how unique this election is," he said.

For Miller, there's one clear takeaway from the chapter of the 2003 campaign when he leapt into front-runner status.

"Things can change dramatically," he said.