The tension was evident in the body language of two of Canada's political leaders as they arrived for their first debate of the Oct. 19 election campaign.

Thomas Mulcair and Justin Trudeau were the first to arrive on set, but the NDP and Liberal leaders avoided eye contact and ignored each other completely until Green party Leader Elizabeth May arrived.

Trudeau spent time greeting the studio camera operators rather than acknowledge Mulcair was even in the room.

Tensions eased a little as May kissed Trudeau on both cheeks when she walked on set with her daughter, before going over to greet Mulcair and engage him in conversation.

NDP leader Thomas Mulcair, left, Conservative Leader Stephen Harper shake hands after the Maclean's debate Thursday evening. (Frank Gunn/Canadian Press)

Trudeau eventually went over to shake Mulcair's hand, but the awkward delay was a tacit acknowledgment the two are each other's main rivals to replace Stephen Harper as prime minister.

A smiling Harper, accompanied by his son Ben, arrived last, telling moderator Paul Wells he was "glad to be here," before going to greet the other leaders, and making small talk with Trudeau.

"Welcome, prime minister," Trudeau said.

"Justin, did you go on campaigns when you were younger?" Harper asked. Trudeau responded with an anecdote about travelling with his father on a train in the 1980 campaign.

Harper provided one of the evening's few lighter moments when he knocked over his glass of water just before the debate began, and stooped to wipe it up before a Rogers staffer stepped in to do the job.

Family visits

Once the questions began, Harper — on the far right podium — spent most of his time standing sideways to face the other leaders as they spoke, and only turned to the camera when he was speaking.

Trudeau, on the far left podium, and May next to him, both pivoted to look at whomever was speaking, but Mulcair spent almost the entire evening staring straight ahead or looking down. Only once or twice did Mulcair actually turn to face Harper when the Conservative leader was directly attacking NDP policies.

At one point, as May and Harper stood facing each other while squaring off on the economy, Mulcair ignored them and looked straight ahead, leaving the impression they were debating around or through him.

During the first commercial break, both Trudeau and May greeted Ben Harper, who came in to chat briefly with his father. In another break, while the make-up artists touched up each of the leaders, May got a long hug from her daughter.

The leaders' rarely referred to notes, but on occasion May would scribble something new, usually when Harper was speaking, and more than once the Green leader looked bemused as the three men talked over top of each other.

Harper, who was the target of most of the attacks during the debate, smiled or smirked at most of the vitriol directed his way, only occasionally waiving an arm to the moderator to indicate he was anxious to speak to a point just raised.

Each leader appeared calm and relatively relaxed during the breaks and none appeared at any point to be flustered or frustrated with their performance.