While the Conservatives have made significant inroads in Quebec over the last decade, clinching a seat in Montreal and the surrounding area is a feat that has eluded Harper, though not for lack of trying.
The Conservatives have gradually chipped away at the Liberals' share of the vote in Mont-Royal, with Saulie Zajdel, in 2011, coming within 2,300 votes of unseating Liberal MP Irwin Cotler, who has held the riding since 1999. Cotler, a human-rights lawyer with international credentials, announced earlier this year he is retiring from politics.
Zajdel was given an advisory role with the party following the 2011 federal election, but was later arrested and charged as part of a provincial anti-corruption sweep in 2013. In May, Zajdel pleaded guilty to charges of breach of trust and corruption in connection with two real estate deals.
Robert Libman, a well-known English-language rights activist and former MNA, won the Conservative nomination in April. Libman, former mayor of Côte Saint-Luc, is running against the municipality's current mayor, Liberal Anthony Housefather. Old political rivals, both men have name recognition in the riding and both want Cotler's seat in Parliament.
Harper will travel from Ottawa to Mont-Royal by bus for a 5 p.m. ET rally, where he will give a speech flanked by Libman and the rest of his Quebec team.
Here are 5 unofficial reasons why Harper is in Mont-Royal today:
1. Drawing battlelines
A longstanding Liberal bastion, Mont-Royal was held for nearly 20 years by its best-known MP and former prime minister, Pierre Trudeau.
Today, the ridings that border Mont-Royal are held by Harper's political rivals: Papineau, which has been held since 2008 by Liberal Leader Justin Trudeau, the eldest son of the late prime minister, and Outremont, which NDP leader Tom Mulcair snatched from the Liberals in 2007.
In his speech, Harper will continue to tout his party's positions on the economy and public safety — battlelines he began to draw earlier this year.
"In this election, Canadians will face a clear choice between Prime Minister Stephen Harper, who has the proven experience today to keep Canadians safe and our economy strong, Justin Trudeau, who is just not ready to be prime minister, and Thomas Mulcair, who is a career politician who does not even know what the tax rate is in Canada — he just knows he wants to raise it," Harper spokeswoman Catherine Loubier said in an email to CBC News that repeated the Conservative Party's well-worn messaging.
2. Support for Israel
Harper's stance on Israel has locked-in the support of many Jewish voters, who account for at least one-third of the population in Mont-Royal.
Whether Israel is a wedge issue between Harper's Conservatives and Liberals under Trudeau remains to be seen.
Housefather, the Liberals' candidate in the riding, publicly praised Trudeau for his "unequivocal support for Israel" following a town hall meeting at Shaare Zion Congregation less than two weeks ago.
"[Trudeau's] unequivocal support for Israel, his confirmation that our voting pattern on Israel at the United Nations won't change, his condemnation of BDS (Boycott, Divestment and Sanctions) as a new form of anti-Semitism and his clear statements that we will judge Iran on its actions not its words were very much appreciated," Housefather said in a post on Facebook July 23.
3. No hard feelings!
Housefather and Libman did not start off as party establishment favourites, but both won the nomination thanks to hard work and grassroots support.
Jonathan Goldbloom, son of former provincial Liberal candidate Victor Goldbloom, was seen as the party's choice, while the Conservatives signalled they would have preferred Pascale Déry, a former television journalist, who could have helped them with the Francophone vote.
However, once their nominations were in hand, their respective parties were quick to rally around them.
In addition to holding a rally in Mont-Royal today, Harper dispatched his wife, Laureen, to the riding this past week for a private event organized in Libman's honour.
4. Montreal 'marginalized'
Asked about his party's fortunes in the province, Harper said he was "optimistic" Quebecers would give the Conservatives "another chance."
In an interview with Montreal's CJAD radio in May, Harper said that having the NDP or the Bloc representing the interest of Quebecers had resulted in nothing more than "Quebec, and particularly Montreal, being marginalized in federal politics. We don't want to see that," Harper said.
"We want to see Montreal, the second biggest city in the country, we want to see it at the cabinet table."
5. Ready 'to fight' uphill battle
Asked whether the Conservatives had all but given up on winning a seat in Montreal, Harper told CJAD radio "I wouldn't say that."
"Obviously, if you look at data we've got, chances are better in Quebec City... Montreal's been tougher, but we're going to fight in every riding across the province."
Liberals are strongly favoured to win Mont-Royal, according to seat projections updated on July 31 by polls analyst Éric Grenier, the founder of ThreeHundredEight.com.
"All things being equal," Grenier told CBC News, "the Liberals have a 78 per cent chance of winning Mont-Royal if an election were held today."
Grenier's seat projection model makes individual projections for all ridings in the country, based on regional shifts in support since the 2011 election, and taking into account other factors, such as incumbency.