"Take This Waltz," Directed by Sarah Polley Margot (Michelle Williams) and Daniel (Luke Kirby) meet on a trip to Louisbourg, Nova Scotia, site of an 18th-century French fort and a present-day National Historic Park. They sit together on the flight home to Toronto, and the attraction between them is obvious and mutual. This makes it a bit awkward when they discover, sharing a cab from the airport, that Daniel lives across the street from the charming, cozy row house where Margot lives with her husband, Lou (Seth Rogen). Margot is not eager to give up her infatuation with her broodily handsome neighbor. Nor does she want to destroy her marriage, which in spite of moments of frictions and miscommunication, is playful and affectionate. Mr. Rogen turns his natural clowning charm into an aspect of Lou's personality that is, for Margot, both comforting and annoying. Daniel, for his part, does not push himself on Margot but does not exactly push her away either. He hovers in the middle distance, letting her know that he is interested and available should her ambivalence resolve in his favor. That ambivalence in the principal subject and dominant mood of "Take This Waltz," Sarah Polley's honest, sure-footed, emotionally generous second feature. Ms. Williams, one of the bravest and smartest actresses working in movies today, portrays a young woman who is indecisive and confused, but never passive. Margot's uncertainty, as she and Ms. Polley understand it, is a kind of passion in its own right. The current of her desire runs strongly in two directions: toward the man she knows and loves, and toward the stranger she wants in ways beyond her immediate understanding. Margot is stubborn, decent and disciplined, but also selfish, needy and coy. Nobody in this film is just one way. Ms. Polley, as a writer, a director of actors and a constructor of images, excels at managing the idiosyncrasies and contradictions of her characters so that our knowledge of them is both intimate and mined with potential surprise. Margot and Daniel don't know what they are going to do, and Lou does not know what is happening, and for most of the movie we dwell in a similar state of suspense and partial knowledge. We also find ourselves in a richly imagined, highly specific place. Toronto, which has obligingly impersonated just about every other North American city for decades, is here given the chance to play itself, to show off its special blend of dowdiness and sophistication. Speaking of the glories of Canada, "Take This Waltz" is also a tribute to the genius of Leonard Cohen. The title is taken from one of his songs, which accompanies an astonishing (and very sexy) montage late in the film. We also hear, at another crucial point in the drama, the Nova Scotia-born singer Feist's ebullient, uncompromising cover of "Closing Time." But not "Hallelujah," which Mr. Cohen himself has said is overused in films and on television. The lyrics to that song nevertheless contain a line that resonates through Ms. Polley's movie: "All I ever learned from love was how to shoot somebody who outdrew you." In other words, how to turn vulnerability into advantage. How to cheat. The wounding power of love, its essential asymmetry and unfairness, permeates "Take This Waltz." The one thing you know for sure is that someone - maybe everyone - is going to get hurt. And yet the film is neither depressing nor melodramatic. It is full of music, color and warmth, some of it supplied by a supporting cast that most notably includes Sarah Silverman as Lou's wise and troubled sister Geraldine. The story takes its time unfolding and pauses to linger over funny, odd and touching details. The camera (Luc Montpellier is the director of photography) is as sensitive as Margot herself to nuances of feeling and perception. Ms. Polley's debut feature, "Away From Her," was based on an Alice Munro short story, and Margot, with her mix of good sense and capriciousness, resembles some of Ms. Munro's heroines. In a Munro story the men might not be as nice, but the balance of clarity and compassion in "Take This Waltz" suggests that this writer continues to exert an influence over Ms. Polley. As a filmmaker she is good at subtlety, and also at obviousness. There is a striking scene in a swimming pool shower room where Geraldine, Margot and another friend chat idly about sex, marriage and other matters. A group of older women is in another part of the room, and Ms. Polley cuts from one set of naked bodies to the other, noting the contrasts of size, shape and firmness. It's hard to miss the point - young flesh will age; old flesh was once young; time wins in the end - but it's a point worth making. The last section of the film may seem a bit fuzzier. There is a moment about 90 minutes in that I was sure was the end, and I still think that stopping there would have made "Take This Waltz" perfect. But I'm also willing to grant that perfection may not have been Ms. Polley's chief concern, especially since the great theme of this wonderful movie - a source of delight as well as distress - is that imperfection is all anyone ever learns from love. "Take This Waltz" is rated R (Under 17 requires accompanying parent or adult guardian). Sex, implicit and explicit. Take This Waltz Written and directed by Sarah Polley; director of photography, Luc Montpellier; edited by Christopher Donaldson; music by Jonathan Goldsmith; production design by Matthew Davies; costumes by Lea Carlson; produced by Susan Cavan and Ms. Polley; released by Magnolia Pictures. Running time: 1 hour 56 minutes. WITH: Michelle Williams (Margot), Seth Rogen (Lou), Luke Kirby (Daniel), Sarah Silverman (Geraldine), Jennifer Podemski (Karen) and Diane D'Aquila (Harriet).