Patrick Brown's abrupt resignation as Ontario Progressive Conservative leader has not only thrown his party into turmoil with an election on the horizon but it's also disrupting election plans for the Liberals and NDP.

The campaign is due to start in May with a vote on June 7. Liberal Premier Kathleen Wynne was preparing to fight off Brown's very real threat of unseating her but now he's vanished and the party needs a new leader.

Wynne and NDP Leader Andrea Horwath have no idea who their opponent is going to be and that means they, too, are in a holding pattern while the PCs have a leadership race.

Brown stepped down following a media report that contained allegations of sexual misconduct. Brown denied the allegations and none have been proven in court.

"For the last six to nine months, parties have been busily preparing their campaign plans," said Kathleen Monk, a political commentator and strategist who worked for former federal NDP leader Jack Layton.

Brown speaks at a news conference at Queen's Park in Toronto on Jan. 24, 2018, a few hours before he stepped down as Ontario Progressive Conservative Party leader. (Aaron Vincent Elkaim/Canadian Press)

"We knew the cast of characters. All of a sudden, the cast of characters has changed," said Monk.

"We don't know who the third player is and that's significant."

Doug Ford kicks off the race

When Wynne and Horwath talked to reporters a few hours after Brown's resignation in their offices at Queen's Park, they were reluctant to comment on how his departure affects their campaigns. They both wanted to keep the focus on the issues of sexual harassment and violence against women and what to do about it.

But behind the scenes, their strategists are likely talking over potential scenarios. What if they are up against someone like Doug Ford? The former Toronto city councillor and brother of the late mayor Rob Ford announced Monday that he is going for the job and wants to be premier.

Running against Ford will require different strategies than running against someone like Caroline Mulroney, the daughter of former prime minister Brian Mulroney who is being urged to put her name forward. While they both come from political families, their resumes and personalities differ greatly.

Campaigns do opposition research on their competitors so they are ready to attack, if and when necessary. Until the Liberals and NDP know who the PC leader will be, they have to prepare for various candidates or wait until he or she is chosen and then act quickly.

Former Toronto city councillor Doug Ford holds a news conference in Toronto on Jan. 29, 2018, to announce his intention to run for leader of the Ontario Progressive Conservative Party. (Frank Gunn/CBC)

The PCs will choose their leader by the end of March, with the campaign officially starting just a few weeks later.

War rooms must be 'nimble'

"There is no doubt that whoever the PCs do pick will factor into the campaign strategies of the NDP and the Liberals and their war rooms," said Robin MacLachlan, a political commentator and vice-president at Summa Strategies in Ottawa.

"They will have to be nimble."

The new PC leader might change parts of the party's platform, which was released in November and has Brown's face on the cover of it.

The Liberals and NDP have had plenty of time to pick it apart. If changes are made, the parties will have to adapt and prepare new responses.

Wynne speaks to media in her office at the Ontario legislature on Jan. 25, 2018, following Brown's resignation as PC leader. (Frank Gunn/Canadian Press)

"There is a lot of uncertainty," said David Herle, the Liberal campaign co-chair, on CBC Radio's The House.

"We don't 100 per cent know if they are going to stick with their platform."

Herle also said that Brown's departure could improve the PCs' chances of winning in June.

"Frankly, Brown was a weak leader and a weak candidate and I was looking forward to running a campaign against him," said Herle. "And the odds are quite high that they will choose somebody more effective."

Wynne, while a seasoned politician and campaigner, is an unpopular premier and the Liberals trailed the PCs in polls for months. More recently, they have managed to close the gap.

Last week, all indications were pointing to a tough and close election to be fought primarily between Wynne and Brown, with the NDP's Horwath trailing behind their two parties.

NDP could seize opportunity

The NDP was always going to try and pitch its party as the best alternative to the Liberals, but Monk said that message might break through more now that the PCs are in turmoil.

"I think where Andrea and the party have an opportunity in what's happening is that if you want a change from Kathleen Wynne, now really Andrea is your only other choice because that party is in such shambles," she said.

"Certainly any political seismic activity like what's just happened in the last few days is going to affect the election results and does create opportunity but it's how the party and campaigners use it to galvanize people around her," said Monk.

Horwath speaks to reporters in her office at the legislature on Jan. 25, 2018, after Brown's resignation as PC party leader. (Frank Gunn/Canadian Press)

Even some Conservative strategists acknowledge Brown's resignation could work in the NDP's favour.

"This may be the first glimmer of hope for the NDP campaign team that they have a realistic shot," said Chad Rogers, who works with Crestview Strategies.

"They win it by default," said Rogers, who has worked on campaigns on all political levels.

The NDP publicly says it plans to remain focused on its core issues and it doesn't matter whom the PCs elect as leader.

"We are very focused on what we are campaigning for, not what we are campaigning against," MPP Peter Tabuns said Tuesday.

NDP officials say they didn't have any Brown attack ads ready to go, but some third parties were ready to take aim at Brown on the airwaves.

The union-backed group Working Families Coalition already ran attack ads against Brown last year and was set to wage its own campaign against him this spring to keep the PCs out of office. The group now says it is taking a "wait-and-see attitude to see how things shake out."

All parties agree there is uncertainty ahead, but as MacLachlan put it, one thing is certain: "There is no doubt this is going to be a unique election in Ontario."