CBC News will have live coverage beginning at 9:30 a.m. ET at CBCNews.ca and on CBC Television and CBC News Network.
Harper is to arrive at Rideau Hall at 9:55 a.m. and will then deliver remarks at 10:15 a.m., according to a news release from the Prime Minister's Office.
Once the election is called, Canada's politicians will begin a mid-summer marathon campaign. The election date is set for Monday, Oct. 19.
After his visit to Rideau Hall, Harper is expected to head to Montreal for a rally in the riding of Mount Royal.
NDP Leader Tom Mulcair is scheduled to speak in Gatineau, Que., at 10:30 a.m. ET.
The other two federal leaders are scheduled to be at a weekend pride event in Vancouver. Liberal Party Leader Justin Trudeau and Green Party Leader Elizabeth May are expected to attend that before heading elsewhere to kick off their campaigns.
Voters will get their first chance to see the party leaders together in action on Aug. 6 during a debate hosted by Maclean's magazine in Toronto.
The election campaign, which will last 11 weeks, or 78 days, will be one of the longest in the country's history.
According to The Canadian Press, only Canada's first two election campaigns were longer. The 1867 campaign lasted 81 days, while the 1872 campaign went for 96 days. Back then, voting was staggered over the country for a period of several months.
The longest race in recent history was a 74-day campaign back in 1926.
A long campaign is seen as benefiting the Conservatives, who are acknowledged to have the biggest war chest.
During a typical 37-day election period, each party can spend a maximum of $25 million. For each additional day, that limit is increased by 1/37th, or an extra $675,000, meaning an 11-week campaign would allow parties to spend more than $50 million.
Individual candidates also get an additional $2,700 a day to add to their usual limit of approximately $100,000.
A longer campaign will also cost Canadian taxpayers more. By Elections Canada's estimate, a traditional five-week, 35-day campaign costs about $375 million to run. Parties are also reimbursed for half the money they spend during an election campaign.
Seeking 4th mandate
The Conservatives under Harper are seeking a fourth consecutive mandate, while Mulcair and Trudeau are both entering their first federal election campaigns as the leaders of their respective parties.
A key issue of the campaign will likely be the management of the economy.
Canadian economic growth has stumbled in recent months. Statistics Canada reported Friday that the total value of the country's economy declined by 0.2 per cent in May, the fifth consecutive monthly slide.
More seats up for grabs
The Conservatives hold 159 of the 308 seats in the House of Commons, compared with the NDP's 95 and the Liberal Party's 36.
The Bloc Québécois, the Forces et Démocratie party and the Green Party have two seats each. There are also eight independent MPs and four vacant seats.
However, there are more seats up for grabs this time round. Following the release of 2011 census population numbers, federal electoral boundaries were revised, which led to an increase in the number of seats in the Commons to 338.