The underlying subject of many romantic comedies is chemistry, the mysterious rapport

The underlying subject of many romantic comedies is chemistry, the mysterious rapport that draws people together despite whatever circumstances—being already married, having different sexual orientations—might be working against them. It’s a tough thing to simulate in movies because, well, that’s the nature of chemistry. So What If has a sizable gift in the casting of Daniel Radcliffe and Zoe Kazan, who either have terrific chemistry together or are able to fake it expertly.

In the opening scene, their characters, Wallace and Chantry, bond over refrigerator magnets at a party and he walks her home. She mentions her boyfriend at the usual moment for such things, and that becomes the major impediment to a quick resolution of this mutual-attraction club. They are in Toronto, which actually plays Toronto here, not an unnamed U.S. city. Chantry is an animator, which unfortunately means there are cartoon episodes in the film; longtime beau Ben (Rafe Spall) is about to depart for a six-month work contract in Dublin. Wallace is working a dull job after dropping out of med school because he caught his girlfriend cheating; now he’s living with pal Allan (Adam Driver, from Girls), whose new affair with Nicole (Mackenzie Davis) isn’t helping Wallace’s mood.

Elan Mastai’s script—based on a Canadian play—depends on keeping the two leads apart, which can be a labored ploy (one third-act delaying tactic isn’t remotely credible), but can also result in the occasional When Harry Met Sally rom-com success. If you can roll with said ploy, you will notice that the wisecracking zingers and cascading conversations rarely pause, and that when a quiet moment is required—a pause in the moonlight before deciding to skinny-dip, for instance—the film can handle it.

The cast is crammed with people who can deliver dialogue. Driver is consistently droll, and Megan Park delivers sidekick laughs as Chantry’s sister, who would not be averse to a fling with Wallace if Chantry isn’t going to act. Radcliffe makes his somewhat pinched charm work nicely here, if there were still any doubt that he’s quite capable outside the Harry Potter universe. Kazan, late of Ruby Sparks, continues to impress, not least because she gives a very amusing physical performance. Director Michael Dowse’s previous film was Goon, a funny hockey picture, which suggests his Canadian corner is a lively place to make movies right now. Opens Fri., Aug. 8 at Meridian and Lincoln Square. Rated PG-13. 97 minutes.

film@seattleweekly.com