Casting agents of independent cinema, take note: If Kristen Stewart is too busy or expensive for your project, Swedish newcomer Erika Linder is more than happy to step in. Evoking the new arthouse queen’s balance of sullen and sultry with a fluency that borders on outright imitation, the 26-year-old model’s big-screen debut carries more charge than everything around her in “Below Her Mouth,” a sexually frank but narratively flimsy girl-meets-girl romance that never gets under its gorgeous characters’ amply exposed skin. Rather indifferently charting the expected emotional fallout of the lightning-bolt attraction between brooding roofing contractor Dallas (Linder) and sexually undecided fashion editor Jasmine (Natalie Krill), Canadian helmer April Mullen’s good-looking film only snaps fully to attention in its humid love scenes. It may find a small, appreciative audience in the LGBT market, the “L” quadrant of which remains critically neglected on screen.

“Even inanimate objects aren’t safe from you,” a coolly discarded lover (Mayko Nguyen) tells Dallas as a final kiss-off after their breakup at the film’s outset. It’s one of many lines in Stephanie Fabrizi’s original screenplay that sounds both intriguing and not quite like anything a real person might actually say, though it does at least give the audience fair warning: Alluring as she looks in chicly androgynous workwear, the prickly, self-oriented Dallas is mighty hard to love.

The next object — an animate one, but as blandly drawn by the script, only just — to learn this is the comparatively prim, proper Jasmine, who falls under Dallas’s disruptive spell just as her life could hardly be fitting more tidily into place. Newly engaged to dreamboat boyfriend Rile (Sebastian Pigott) and plushly settled in the Toronto suburbs, Jasmine is on course for a life of well-dressed domestic bliss when she spots Dallas nailing the roof of a neighbor’s house and realizes — not to put too fine a point on it — that the sexy tomboy’s nailing skills could be applied elsewhere.

In a film not otherwise heavy on humor, there’s a sly wit to the way this premise plays with the hoary conventions of straight pornography, which has recycled variations of the tradesman-and-the-lady setup for decades. And, as in porn, “Below Her Mouth” makes no apology for getting straight to the carnal outcome of this encounter. In the face of Dallas’s bullish pursuit (bordering even on harassment), Jasmine puts up a modicum of resistance, but it’s not too long before the two tumble gaspingly into bed. Cue a series of progressively heated, athletically choreographed sex scenes, with strap-ons and high-pressure bath faucets among the accessories to the action.

Mullen and her stars commit to the film’s erotica with welcome gusto — if only the lovers’ clothed interaction was half as lively. Between bouts of lovemaking, the pair exchange unilluminating confessions about their respective sexual and psychological histories, growing somehow vaguer with each revelation. “I’ve got no emotional stamina for intimacy,” Dallas admits; the film, too, is more preoccupied with the physical. Krill struggles to wrestle much nuance out of Jasmine’s wanly written identity crisis, with the script and camera alike favoring Dallas’s inscrutable perspective. Though given an equally sketchy character to play, Linder throws enough spiky, smoldering attitude at the screen to make her a compelling cipher; it’s a debut hopefully striking enough to command fuller, more testing roles.

Technical contributions are mostly sleek, with Maya Bankovic’s soft, shadowed lensing lending a metropolitan glamor to the bare-brick nightclubs and artfully distressed warehouse apartments of Toronto’s hipster quarter; however the characters resolve the romantic quandary in which they find themselves, you never once fear that their interior decoration — or, indeed, their firmly laid roofs — will suffer.