TORONTO -- When director Kevin Smith came up with the idea for "Zack and Miri Make a Porno" a few years back, he knew right away that he wanted Vancouver-born actor Seth Rogen to star in it.

"I saw Seth in `40-Year-Old Virgin,' fell in love with him, and said: `My god, this dude would be fantastic in a leading role,"' Smith recalled during an interview at last month's Toronto International Film Festival.

Smith began to fret that he might not land his man, however, when Rogen's stunned face began to crop up on billboards all over Los Angeles advertising the 2006 blockbuster "Knocked Up."

It was the "summer of Seth," Smith says, referring to Rogen's other star turn as a careless police officer in the smash teen comedy "Superbad."

"At that point it was a crapshoot whether or not we would get him 'cause he was blowing up from that."'

In the end, of course, Rogen said yes to Smith's film about two friends who plan to make a quick buck by shooting a hardcore movie.

In fact, says Smith, Rogen "rode shotgun" for the entire production, offering up some of his friends as co-stars, and punching up the script with more jokes.

"He's a dirty guy, a filthy dude, so he warmed to the material immediately," Smith jokes. "Mercifully he liked the script and decided to do it."

During the festival, Smith also took time to make a cameo in an episode of "Degrassi: The Next Generation." During an interview on the set of the show, he wore the black trenchcoat that's made him famous as the quiet half of Jay and Silent Bob, the slacker duo from the '90s cult classic "Clerks."

While the pair have made appearances in several of Smith's movies, the director stayed behind the scenes for "Zack and Miri."

Smith says his latest movie received the go-ahead from Hollywood movie mogul Harvey Weinstein based solely on its high-concept title. The pair have worked together since the early '90s producing the envelope-pushing "Chasing Amy" and the controversial religious comedy "Dogma."

Elizabeth Banks co-stars in the film, which also features an appearance by former porn star Traci Lords, who shunned the industry in the '80s after it was discovered she was underage. Lords has since acted mostly in low-budget Hollywood movies.

"It was a total get to have her in the film," Smith says.

Smith says 26-year-old Rogen was full of ideas.

"Even right down to the marketing materials, the dude always has an opinion and usually it's a very good one. It's insane because he's young... and he operates like an old soul," the director says.

"Seth Rogen might very well be my favourite Canadian on the planet right now."

"Zack and Miri Make a Porno" opens Friday.