If you see enough movies, you may start to absorb the lesson that any commercial comedy with the word ''wedding'' in the title is to be avoided. Films like The Wedding Planner and The Wedding Date overlap two flavors: corny and contrived. They tend to be about major life plans going wrong, but even the chaos comes off as overly diagrammed. We keep getting hit over the head with the lesson that happy endings emerge from messy beginnings. When I saw the poster for The Big Wedding, with the grinning, laughing faces of all these famous actors beaming out at me, I thought, ''Wow, this movie will probably waste a lot of talent.'' Surprisingly, though. the actors shine. The movie, in its basic concept, is corny and contrived, but as written and directed by Justin Zackham, it's executed in a pleasantly wry and understated fashion. I bought the people on screen, even when what they're going through is a tinny series of movie-farce convolutions.
Alejandro (Ben Barnes) is getting married to Missy (Amanda Seyfried), and the two couldn't be happier except for one glitchy problem: Alejandro has three different mothers sort of. His parents, Ellie (Diane Keaton) and Don (Robert De Niro), adopted him. Then they got divorced, and Don hooked up with Bebe (Susan Sarandon), who took over raising Alejandro. Now, Alejandro's Colombian birth mother (Patricia Rae) has shown up for the wedding, and she's a pious Catholic named Madonna who doesn't believe in divorce. So for the weekend, Ellie and Don will pretend to be married again, even though they're just the kind of divorced couple who are always one or two tense jokes away from baring their claws.
Like I said: contrived. So what redeems The Big Wedding? It's the way that the actors run with this scenario as if they were in a European art film, one that's more focused on bourgeois behavioral nuance than plot. (The Big Wedding is, in fact, a quasi-remake of the 2006 French film Mon frère se marie.) De Niro, after too many phoned-in performances, has woken back up as an actor. As Don, a sculptor, recovering alcoholic, and seductive ''douchebag'' (it's the word that characters keep tossing at him), he looks terrific in his salt-and-pepper beard, and he's as sly-dog funny and present as he was in Silver Linings Playbook. Don keeps getting punched, insulted, and called out for his years of bad behavior (infidelity, caring only about his ego), but De Niro makes him a Teddy bear of selfishness; you can see why he keeps winning these women back. He and Keaton, energizing her sun-dazed flakiness with pinpoint eruptions of hostility, make this couple seem rooted in experience. They push each other's buttons without trying.
The other performers have one-note roles but do well enough filling them in. Topher Grace is Ellie and Don's other son, a 29-year-old virgin who think he's holding out for love, and maybe he is, but when he meets Alejandro's biological sister (Ana Ayora), a lifetime of hormones catches up with him, and suddenly love and lust don't look too far apart. It's a sitcom setup that Grace plays with elegance. Susan Sarandon, as the temporarily kicked-to-the-curb Bebe, has the tricky job of acting polite and secretly furious at the same time, and she pulls it off. And Katherine Heigl, as Ellie and Don's romantically frazzled but newly pregnant daughter, finds a nice outlet for her trademark neurotic tension. Robin Williams, as a worldly priest, is witty enough to make you wish that this character had his own movie. Zackham keeps the situations whirring as if he were spinning plates, but he's got to be given credit for bringing out his cast members without letting them lapse into shtick. In its airbrushed way, The Big Wedding is onto something: the way that life keeps tearing up the rules that we write. Like, for instance, the one that says commercial wedding comedies are always phony. B