When the terminally adorable Canadian quartet Shapes and Sizes signed to indie-rock über-cutie Sufjan Stevens’s record label, Asthmatic Kitty, the sudden surfeit of sweetness must have been overwhelming. Surely molars crumbled in its wake; blood turned to syrup; insulin waved the white flag. Only an army of tap-dancing Japanese toddlers, baby spider monkeys in matching bonnets, and the teenage Sandra Dee could have upped the awww factor. It was a match made in twee heaven, if not Tokyo. But there’s more to Shapes and Sizes than eight pinchable cheeks and a press photo that looks like something a proud grandma might pull out of her pocketbook. The 10 songs on the group’s self-titled debut are oddly engaging, pitched somewhere between the Fiery Furnaces’ autistic artistry and a community-college production of South Pacific. Sometimes they sound like a ’60s girl group commandeered by Philip Glass; sometimes they sound like Pavement multiplied by the New Pornographers and divided by Eric Dolphy. If that doesn’t make much sense, neither do Shapes and Sizes’ shambolic minisuites and turn-on-a-dime arrangements. Three of the band’s four members write songs, and it sounds as if they compose potluck-style, each bringing in separately written parts, jury-rigging them together, and delighting in the happy accidents that result. Shapes and Sizes is one of those bands that sound as if a single change in lineup might ruin everything, so integral is each member’s musical personality to the collective character. Co-vocalists Rory Seydel and Caila Thompson-Hannant, who also play guitar and keyboards, often sing in unison, an octave apart, and seldom attempt conventional harmonies. Seydel has a strangled, slightly nasal emo-boy tenor; Thompson-Hannant has a sturdy, vibrato-heavy alto that shifts from ingenuous lilting to brassy belting in the space of a chorus. In some of the most effective numbers, the irresistibly incompatible pair trade off lines in the snappy, dialogic manner of musical-theater protagonists, amplifying, contradicting, or complicating each other’s statements. Their colleagues are no slouches, either. Bassist Nathan Gage and drummer/vibes player Jon Crellin, equally adept at skronky jazz and quirky pop, ground the whimsy in roiling rhythmic textures and shrewd counterpoint. Guest musicians augment the cheerful mayhem with tenor sax, trumpet, flügelhorn, viola, and pedal steel. At just over 40 minutes, the CD isn’t long, but it covers a lot of ground. “Island’s Gone Bad” pits Seydel’s seasick vocals against a bleary saxophone, a whiny viola, surfy drums, and Thompson-Hannant’s buoyant warble. While Seydel kvetches about having to scavenge for food and call the parents, Thompson-Hannant blithely declares, “I like eating fruit off of trees when I’m with you/Fruit always tastes much sweeter, and air always tastes much cleaner when I’m with you.” Imagine a mash-up of Blue Lagoon and Lord of the Flies. The ukelele-flecked “Northern Lights” and the galloping, punch-drunk “Goldenhead” are high-drama girl-group anthems, whereas “I Am Cold,” a glacial synth-dirge, is a study in art-rock minimalism. Although the Thompson-Hannant solo tracks are the most hummable, the duets are the most affecting. In “Rory’s Bleeding,” Seydel explores the comic possibilities of self-pity, joining an angelic Thompson-Hannant in singing, “If Rory goes to heaven, we’ll break up the band/We’d be sad, we’d be sad, but it isn’t in our hands.” The lurching, pedal-steel-laced waltz “Boy, You Shouldn’t Have” ends with Seydel begging to be taught “how to not care” and Thompson-Hannant coolly repeating, “I’ll never tell you” and “Wouldn’t you like to know?” It’s very sweet and very funny, and it says a lot without resolving anything, which might as well be Shapes and Sizes’ motto.