The PCs are choosing between a newcomer to provincial politics, Barrie member of Parliament Patrick Brown, and a previously failed leadership candidate, Christine Elliott, the Whitby-Oshawa member of the Ontario legislature.
Each one aims to be seen as the candidate to provide a change in direction for a party that hasn't won an election since 1999.
Elliott was the first in the race, declaring her candidacy less than a month after former leader Tim Hudak resigned, following the Kathleen Wynne Liberal victory in the June 2014 election.
Elliott has received the lion's share of big-name endorsements, including former premier Bill Davis, the vast majority of the PC caucus, as well as former Toronto mayor Rob Ford and his brother Doug.
The Brown campaign has responded by suggesting Elliott is the establishment choice — an establishment that has lost four straight elections.
"The party establishment certainly isn't supporting me," said Brown. "I'm not going to owe them any favours. And frankly I can bring real change to the party that we so desperately need."
'Not where people want us to go'
Judging from attendance at his campaign events, Brown has attracted a large membership base among new Canadians in the Greater Toronto Area, a demographic that the PCs have failed to reach with the same success achieved by the federal Conservatives.
Brown also courted support among those protesting the Wynne government's changes to the sex-education curriculum.
Elliott said she's concerned that if Brown wins "the social conservative group within the party would take over, and I think that's not where people want us to go."
She dismissed Brown as "not what I would call Progressive Conservative," emphasizing the word "progressive."
"If we keep going on the same old hard-right message that we have in the last two elections, we will never win. Never."
The race has focused mainly on the question of who is best suited to defeat Wynne rather than on questions of policy.
The candidates are wary of being perceived as thinking they have all the answers, and critical of how the Hudak PCs alienated voters with a campaign platform of cutting 100,000 public-sector jobs.
Elliott has made the most specific pledge: to reduce Ontario's 11.5 per cent corporate tax rate — already the lowest among the provinces — to 10 per cent.
Competing membership claims
Party officials say 76,587 members were eligible to vote during the two days the polls were open this week. The Brown campaign claimed to have signed up about 41,000 members by the deadline, and the Elliott camp 34,000. But the most recent candidate to drop out, Monte McNaughton, had claimed 12,000 members, so someone (or perhaps all of them) must have exaggerated their numbers.
While each member gets one vote, the party's leadership race rules give equal weighting to each riding. That means a candidate can't expect to win with supporters concentrated in a small number of constituencies. Both campaigns claim their memberships are well-distributed across the province, but this can't be independently verified.
Elliott, 60, is the widow of former federal finance minister Jim Flaherty and a mother of three adult sons. Brown, 36, is unmarried and has no children.
Both Brown and Elliott were elected in 2006 — Brown as the Stephen Harper Conservatives rode to power, and Elliott in the provincial byelection to fill the seat vacated by Flaherty for his federal run.
The winner will become the fourth person to head the PC party in 12 years. Ernie Eves lost the 2003 election to the Liberals under Dalton McGuinty, as did John Tory in 2007 and Hudak in 2011.
Hudak also lost an election to the Wynne-led Liberals in 2014.