The smokers, who sued on behalf of 2 million smokers, charge Imperial Tobacco, JTI MacDonald and Rothmans Benson & Hedges with pushing the addictive habit despite the health risks.
The civil trial in Montreal could take more than a year.
The Canadian Broadcasting Corp. reported a few plaintiffs spoke to reporters during a break in the proceedings.
"Smoking was in fashion. I chose to smoke to show I was 'in,'" said plaintiff Cecilia Letourneau.
"Everyone smoked back then. To be like the others, I smoked. And I got hooked pretty fast," said Jean-Yves Blais, who began smoking when he was 10.
Deborah Glendinning, an attorney representing Imperial Tobacco, said the plaintiffs bear some of the responsibility for their decisions.
"Just because it's a legal product doesn't absolve us of liability, but just because there's risks and dangers associated with it doesn't mean we're automatically at fault, either," Glendinning said during a break.
"I'm looking very forward to seeing what kind of proof they can bring because I don't think they've got it and I believe we will ultimately be successful," Glendinning said.