When pressed—okay, when barely asked—Sienna Guillory offers a theory about why people get into acting.

“All actors are naughty,” she declares, throwing her arms upward for emphasis in an otherwise subdued corner of a downtown Vancouver hotel café. “We’re all troublemakers—horrible, attention-seeking children. ”˜Me, me, look at me!’ ”

Actually, the English-born, California-based performer is here to chat about Gunless, a new comedy that opens on Friday (April 30) and marks her Canadian debut. The night before meeting the Georgia Straight, she joined costar Paul Gross, writer-director William Phillips, more cast and crew, and even some horses for the world premiere in Vancouver of the B.C.–shot film, which spoofs gunslinger movies and the code of the West.

An entire Wild West town, Barclay’s Brush, was built in Osoyoos, where the cast hunkered down last year to realize Phillips’s vision, which mirrors Canadian-American personality clashes that persist more than a century later. Guillory plays the surprisingly tough English beauty who challenges Gross’s on-the-run Yank to drop his pistol-happy—not to mention endlessly wisecracking—ways after he’s chased across the border.

“I’m always the straight man,” says the red-tressed thespian, who has played glamorous foils in British comedies such as Love Actually and Rabbit Fever, and action hotties in fantasy-themed items like Eragon and Resident Evil: Apocalypse. “And I’m the tits,” she adds with a Benny Hill eye-roll.

“They usually edit out the scenes where I’m really abrasive, but here I did get to be somewhat obnoxious. In Gunless, I play the adult in a tale about taming a wild man, or taming the wild North, or something. So I couldn’t go too crazy.”

Playing opposite the gunslinging Gross, she says, made it hard to stick to the original script.

“Paul is irrepressible. Fortunately, the writing was terrific and we only elaborated on it when we couldn’t help it, or when there was something clever to add. But I wouldn’t say improvisation was encouraged, exactly. The problem is that we’re constantly trying make each other laugh. You want to make the others feel uncomfortable, because that cracks them up, but you don’t want to cross a line that will ruin the story. And we wanted to keep it suitable for the whole family.”

This indelicate dance is evident in the film’s unusually boisterous end-credit blooper reel, which conveys how difficult it was for the Gunless guys and gals to keep their comedy straight.

Currently, Guillory, who sometimes comes across as a funkier Cate Blanchett, is also willing to be stared at on-stage while playing bass in a Los Angeles groove band. She got the instrument, and some of her talent, from Isaac Guillory, the late Cuban-born musician who married her model mother, Tina Thompson.

Next up for the itinerant Brit is the female lead in The Big Bang, opposite Antonio Banderas.

“I play a stripper,” she says. “What else is new?”