Media coverage of leaders' debates nearly always make reference to a knockout punch, especially since, more often than not, it's never delivered.

So let's give some points to Liberal Leader Justin Trudeau as he preps for Thursday's first debate of campaign 2015 by spending the morning at a boxing gym.

To spar, get it? To show that he can deliver solid blows, as he did in his famous bout with one-time Conservative Senator Patrick Brazeau a few years back, and even take a punch while he's at it.

There's no doubt Trudeau will absorb a few shots when he takes the stage with NDP Leader Tom Mulcair, Conservative Stephen Harper and the Green's Elizabeth May tonight.

Like Mulcair, the debate sponsored by Maclean's magazine and Rogers Media will be Trudeau's first. It's an unfamiliar stage for him, even though the other sides are painting him as the favourite.

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You can watch the Maclean's debate live at 8 p.m. ET in English on City-TV, in English and French on CPAC and in Italian, Punjabi, Mandarin and Cantonese on OMNI TV, and on YouTube.

According to Harper's spokesman, Kory Teneycke, the Liberal leader will exceed expectations by just showing up "with his pants on." Really?

New Democrats are offering a similar, if less evocative, assessment that Trudeau's previous life as a drama teacher will serve him well on stage.

It all adds up to a surprising amount of posturing ahead of a debate that's taking place just five days into the longest Canadian election campaign in anyone's memory.

And it's only the first of four, possibly even five debates, that will be held before voters finally go to the polls on Oct. 19.

First impressions

Still, first impressions are important, even if viewership is likely to be low in the middle of summer, and some networks, like CBC/Radio-Canada, will not be broadcasting it live.

Political strategists believe the debate could establish the narrative for the first half of the campaign — whether it's change versus stability, proven leadership versus risky alternatives — because the second debate won't be held until the middle of September.

Liberal Leader Justin Trudeau warms up in the ring during a photo op at Paul Brown Boxfit in Toronto Thursday prior to the first leaders' debate. Conservative spin doctors say Trudeau would clean up at the debate if he simply shows up with his "pants on." (Aaron Vincent Elkaim/Canadian Press)

Likewise, more debates won't mean a miscue will be less significant as there will be no one else to blame for a mistake. No one else to point to if you are bested in a one-on-one exchange.

A leader who falls into either of those two categories — bested or factually-challenged — should expect to see, read and hear about it. A lot.

It's one of the reasons the party leaders have been engaged in weeks of intense preparations, devouring briefing books and testing out lines. Rehearsing with stand-ins for their political opponents, practising where to look, even how to control their faces when the cameras are on.

For them, it's about winning. Or, at least, not losing.

The debate is divided into four broad segments. First up is the economy. That exchange will be followed by energy and environment, then a segment entitled institutions of democracy (read Senate here), and finally foreign policy and security.

There are points to be scored in these segments by all four leaders. With that in mind here's a brief cheat sheet of what to look for heading into the debate.

The real target

Stephen Harper. Forget all the pre-debate posturing about Trudeau, Harper is the real target.

He's the one with the most experience in these debates. He's also the one with the most to lose after being in power now for nearly a decade.

If this election ends up being really about change versus the status quo, the Conservative leader needs to show off a truly superior grasp of the issues to convince viewers that proven, experienced leadership is the only choice.

Andrew MacDougall, a one-time communications director for Harper, says his former boss also needs to remember his audience.

"It's Canadians you are speaking to, so be calm and measured. His message is 'I'm experienced. I've fought the tough battles.' It's about conveying that through a calm tone and demeanour.''

Tom Mulcair. There's no question that Mulcair is a tough opponent in the uber-partisan confines of daily question period.

He's shown, in that forum, that he can go nose-to-nose with Harper. And Conservatives privately acknowledge that the NDP leader is the toughest opponent they've faced.

Expectations will be high.

New Democratic Party Leader Thomas Mulcair and his wife Catherine Pinhas launch the NDP campaign on the weekend. He needs to look like a statesman, his supporters say. (Christinne Musch / Reuters)

But this time Mulcair won't only be doing the asking. He'll have to do some answering. In 2011, then Liberal leader Michael Ignatieff seemed stuck in the role of opposition leader. Mulcair can't make that same mistake.

In addition, he has to show that he's a better agent of change than Trudeau. That he is the logical choice of voters who want an alternative to the Conservatives.

And then there's that whole, "scary NDP" thing he will have to confront.

"He needs to come out looking like a statesman. Like a prime minister,'' says former NDP strategist Ian Capstick. "And like somebody you can trust with your finances and your job. That's an incredibly difficult feat for a New Democrat."

Justin Trudeau. He's outlined his party's platform already, making it — and him — a convenient target for his opponents. He will need to defend his positions, and to convince swing voters who abandoned the Liberals in recent elections to return.

Most importantly, his performance Thursday will be an important indicator of whether he's the political lightweight as portrayed by the Conservatives; or a new generation of leader with a firmer grasp of the issues than his opponents would have you believe.

Elizabeth May. The only woman on the stage, this debate represents her only chance to join the other leaders since she's not been invited to the other debates.

It's a powerful incentive and expect her to make the most of the opportunity and exposure.

So let the sparring begin. Round one in this match is set to go. Who knows, maybe one of the four leaders will even deliver that highly-elusive knockout punch.