​Stephen Harper has an appointment at Rideau Hall Sunday morning, where he's expected to trigger an 11-week election campaign in advance of an Oct. 19 vote.

An advisory from the Prime Minister's Office says Harper is scheduled to meet with Governor General David Johnston at 10 a.m. ET.

If Harper indeed asks Johnston to dissolve Parliament, it would touch off a rare summer campaign that promises to stretch nearly three months — the longest in more than a century.

It's also expected to be the costliest campaign ever, as well as the first in which three parties all have a legitimate shot at winning — a sure formula for a vicious, no-holds-barred battle.

Harper stands to become the first prime minister since Sir Wilfrid Laurier in 1908 to win four consecutive elections.

He's expected to get the Conservative campaign underway at a rally later Sunday in Montreal, while Liberal Leader Justin Trudeau will be in Vancouver to attend that city's Pride parade.

An advisory from the NDP says Tom Mulcair will launch the New Democrat's "Campaign for Change" Sunday morning in Gatineau, Quebec shortly after Harper's meeting with David Johnston.

On Friday the New Democrats made it clear that Mulcair would not take part in any leaders' debates that didn't include Harper.

So far, the New Democrats have said little about their plans, other than on Friday, when they made it clear they would not take part in any leaders' debates that didn't include Harper.

Such an unusually long campaign would allow parties and their candidates to spend more than double the spending limits of $25 million and $100,000, respectively, that would have applied for a minimum 37-day campaign.

Impoverished rivals

Having amassed vastly more money than any other party, the increased spending limits give the Conservative party and its candidates a huge advantage over their more impoverished rivals.

It's been clear for weeks how the ruling party intends to use its financial advantage: to carpet bomb the air waves with attack ads.

Conservative ads trashing Liberal Leader Justin Trudeau as "just not ready" to be prime minister have been ever-present on radio and television for more than two months already. Liberal insiders admit they've been effective, contributing to the Liberals' slow decline in the polls to third place from their front-running status over the previous two years.

Late Friday, the Conservatives suddenly turned their sights on NDP Leader Tom Mulcair with similar attack ads depicting him as an unethical, opportunistic "career politician." Having helped drive Liberal support to the NDP, they've now evidently decided they need to blunt Mulcair's momentum at the outset of the campaign.

Two-front war

The shifting targets of the Tory ads reflect the tricky two-front war facing the governing party.

At a time when the economy has tanked and polls suggest two-thirds of the electorate are looking for a change, the Conservatives risk driving change seekers to coalesce behind the NDP if they attack the Liberals too hard, and vice versa. They'll attempt to strike a balance, attacking both and warning that the economy is too fragile to risk putting it in the spendthrift hands of either Mulcair or Trudeau.

But Mulcair and Trudeau also face two-front wars — with each other as much as with Harper. Each will be attempting to prove that his party is the vehicle that can defeat the Conservatives and provide real change. And in doing so, they'll be fighting not just to win the election but, potentially, for the very survival of their respective parties.

Should Harper win a minority, the two opposition parties will come under pressure to form a coalition to snatch power from him. Should he win another majority, they'll come under pressure to merge outright and stop splitting the progressive vote.

In either scenario, the opposition party that emerges strongest on Oct. 19 will have the upper hand; the weaker party could face possible extinction.