In Ottawa, the Liberals will select a new — and likely very different — leader. In Montreal, the Opposition New Democrats will use their policy convention to retool the party's message and policies to better suit a government in waiting.
And the Conservatives will begin cranking up their famously effective defensive machine to keep both at bay.
NDP Leader Tom Mulcair is billing his party's event as a critical moment.
"I'm confident that whether it's on renewing the terminology in the (party) constitution or giving ourselves exactly the vision and determination we need to carry this through in the next election, it's going to be a great weekend for us," Mulcair told The Canadian Press.
Stacked up against Sunday's Liberal leadership results-fest, with presumptive front-runner Justin Trudeau the centre of attention, the constitutions, resolutions and workshops of an NDP convention might seem dry. Both parties insist the timing was pure coincidence.
But history has shown that policy conventions can be game changers for parties with brand troubles — even propelling some to future victory. Tony Blair's New Labour in the UK, or even Stephen Harper's Conservatives, both had crucial, moderating policy conventions before winning elections.
Anne McGrath, former chief of staff to late NDP leader Jack Layton, said all social democratic parties come to a point where they need to modernize and consider how they're perceived by the public.
"It's not going to be just about what resolutions get adopted, it's going to be about how we actually conduct debates, and what the consciousness is of the people that are there about the importance of presenting the party as a replacement for this government," said McGrath, now managing director of Ensight Canada.
The NDP rank and file will vote on a change that's been haunting conventions since 2009 — modernizing the preamble of the party's constitution.
A panel of party wise men and women came up with a more moderate statement that drops numerous references to "socialism" and "socialist," as well as the document's anti-free market language.
Leader Tom Mulcair has been disdainful of the old turns of phrase, many of them with roots in the Canadian Co-operative Federation (CCF) of yore.
"We'll continue to fight for labour rights, but we're also going to start making sure that we also put on the table a vision for how to have a sustained economy where were not taking everything for our generation and leaving nothing but debt for future generations."
The NDP's discussion mirrors to some extent the debate Britain's Labour Party had at a convention in 1994, with new leader Tony Blair leading the charge for the party to abandon a constitutional clause that committed to "social ownership."
The discussion in the Labour party had preceded Blair — his predecessor John Smith had already started laying the groundwork. Similarly, Layton's slow, delicate efforts to move his party more towards the centre predated Mulcair's leadership.
Longtime NDP observer David McGrane, a political science professor at the University of Saskatchewan, said he'll be looking for some of the same trends inside the NDP as with Blair's New Labour party — a moment where the party membership accepts the need to become moderate.
"There has been a culture change within the NDP itself, and it's matured in a lot of ways ... if the vast majority of delegates are onside with this, that shows a sort of culture change," McGrane said.
"They're accepting a modernization, but also a professionalization of the party, the idea that the party needs to have a good marketing skills, and they start with putting together a good preamble — one's that quite wishy-washy, actually."
But even if the NDP gets a handle on a more moderate offering for voters, there is the Trudeau factor to contend with. The popular son of former prime minister Pierre Trudeau has been giving the party new buoyancy in recent polls.
Mulcair might like to model his NDP on the success of New Labour in Britain, but the parallels between the charismatic Blair — only 43 when he was elected prime minister — and 41-year-old Trudeau might be easier to draw.
Mulcair, for his part, said he remains unperturbed.
"There's an old saying that a week is an eternity in politics. That leaves 125 eternities between now and the next election," he said.
"It takes constant hard work, that's the only formula I know, and we've got to keep our eyes on the prize. We know that what we can do for the first time is form an NDP government, a progressive government, one where nobody is left behind."
As for the Conservatives, they'll be watching both the Liberal and NDP processes closely — and taking notes on perceived weaknesses.
Finance Minister Jim Flaherty issued a statement this week condemning some of the policy proposals the NDP has put forward for discussion this weekend.
One resolution, for example, calls for the party to support the withdrawal of Canada from NAFTA and the World Trade Organization. Others call for the nationalization of the oil industry and big banks. It remains to be seen whether those resolutions, among others, will make it to the convention floor for general debate.
"Considered in their totality, the NDP proposals would fundamentally change Canada from a market-based democracy to one resembling a command-economy socialist state — like those that so spectacularly failed in the last century," Flaherty wrote.
"The fact that the NDP is actively promoting this utterly discredited economic model at their national convention raises serious concerns about their support for Canada’s proud and long traditional of being a market-based democracy centred on free enterprise."
Also on HuffPost