Eugene Levy does not look quite comfortable, standing on the sofa. Those Groucho brows are frowning, surprised eyes wide. He knows the photos will work better if he's three feet up, and he's much too polite to gripe. But he's wary. That cushion is just a touch plush. Plus, he's had a run of bad luck lately. Yesterday's fish and chips was followed by emergency dental work. Last winter's ceremony to pick up his Order of Canada medal was interrupted by a kidney stone: "I would rather pass a 15-pound baby."
He climbs down gingerly, folds his legs, looks more zen. In fact, Levy has long pulled off one of the most brilliant balancing acts in cinema. Few are so adept at straddling the super-mainstream and the deeply niche. The press notes for American Pie: Reunion flag up how many of his films have topped $100m (seven – now eight); the mockumentaries he makes with Christopher Guest cement his cred but barely bother the box office. What's really remarkable is that in both genres, he's so similar. The audiences change, the receipts yo-yo, but the schtick remains the same.
Today, Levy is midway through the latest Pie's European tour - him, Jennifer Coolidge (another Guest/Pie straddler), five once-young bucks and innumerable photo ops involving baked goods. "You're constantly packing and unpacking. After a while you're like: you know what? Not as much fun as I thought it would be. Because you don't get to see the places you're at."
Many years ago, when he smoked, he had a specific hotel drill. "You'd check in, they'd bring the bag up, you get everything set, you ring down, you order up a lovely cocktail and you sit there and have a leisurely cigarette and sort of look around the room. That would be it. And then you'd maybe make a phone call to say: yes I'm here, and then have another cigarette. But now really the ritual is you get your stuff unpacked you, figure out what you have to have pressed, how quickly you need it and that's pretty much an ongoing thing day to day, trying to figure out what you need. But this place - " he rolls his eyes round the room - "it's phenomenal." Did he know it was a former MI6 building. "This what I'd heard. It makes you think: what's in the walls?" The eyebrows rise, the sides of the mouth, too. Or who, right? "Yes," he nods, that faint flicker of worry returning.
John Candy, with whom he wrote and performed on sketch show Second City Television, said Levy went to work like a banker. He still does. "I like to have a regime," he confirms. "I don't like to be fancy free." That crisp blazer smacks of discipline, ditto the buffed brogues and hair combed into a stiff brillo. He's old-fashioned, courteous: holds the door, offers me the biscotti that came with his latte, speaks in formal, measured sentences. On screen, his speciality is sober businessmen who tap into happiness (the am-dram dentist in Waiting for Guffman) or standard-issue dads (Pie, Cheaper by the Dozen 2) with strange manias. Off screen, he's the dead spit.
No, he himself would not have liked to be a spy, he thinks. "I think it would be an absolutely intriguing job, except for the danger aspect. That kind of puts a bit of a dampener on the thing. But if you really like feeling good heart palpitations in your work that's probably the job for you. But I've never really done anything that implies any kind of danger. I wouldn't skydive, I wouldn't deep sea dive, I wouldn't parachute. I think you're really just rolling the dice. Who packed your chute the night before? Were they hungover?"
The son of a car plant foreman, Levy was born in Ontario in 1946, and fell into film through TV comedy; first behind the screen, increasingly in front. At college he studied sociology – surely not so much of a leap from character acting? "It seemed to be when I was taking it. The only thing I learnt was what "recidivism" means. I've never really got to use the word, but at least I know what it is."
Yet he remains tight-lipped when asked for a definition of "diving for dollars" – a bedroom manouver his character in American Pie: Reunion recommends to his sexually stagnant son (Jason Biggs). He also declines to draw a diagram. "It's better left to the imagination. It sounds like it could either be fun and at the same time a little nasty."
Reunion finds Jim's dad again sweetly, inappropriately eager to engage with his son's erotic issues, 13 years after the original, in which he supplied him with porn mags. But Jim's dad (he never did have a name) is also now bereaved, lonely and vulnerable. "I love the fact that you can have these sentimental moments in Pie. The audience sees these characters as real people, even if they're goofy or stupid. You can get your laughs, but they have to have empathy and affection. To me it's not so much about how racy the film is, but about being truthful. I haven't really encountered a character in an American Pie film that I thought was not a real character. Have you?"
Maybe some of the support can be a touch archetypal, I stutter. There's a perceptible bristle. "Well, it's interesting; I'd kinda love to know which ones." Levy's discomfort is justified. Pie is easy to underrate, catnip for snoots. And its believability is crucially important to him. "For me as a character actor, these characters have to be real. I'm not a joke guy, I'm not a stand-up comic." It's true: Levy is maybe the most striking-looking straight man in comedy. He's keen to be the average Joe – neither his nationality (Canadian) nor his ethnic group (Jewish) have been the least bit important, he says, in forming his comedic sensibility.
But he will conceed that Pie's influence hasn't been entirely benign. "The dangerous thing about what it's spawned is that sometimes theres a little bit too much emphasis on, y'know, bodily functions. It's the anti-Noel Coward approach to getting a laugh. At some point you can't go any lower. You'll get to the point where you can step over the bar."
With Pie the point was the raunch. "Sex was the thing on everybody's mind. And it got kinda graphic and that's why it cut such a big swathe. But now you have other movies which, no matter what their subject is, feel they have to go there. Film-makers know studio executives will look at the script and say: ooh there's a big laugh. It's too easy."
His scepticism about the gross-out progeny of Pie is small surprise. More so is the scorn reserved for those comedies which ape his and Guest's mockmentaries. He's full of praise for Ricky Gervais, but he's never seen the American version of The Office. "I can't, there's no point. Ricky's truly was done like a documentary. In the States they can't go there. They've got to light it brighter, and the camera can't move in quite the same way because the audience won't stand for that."
He warms to his ire. "It's a horrible way of using the device. They're using a device that they don't truly understand. And I'm not a fan of kind of doing something. Do it or don't do it. If you're going to do a fake documentary, make it a fake documentary. Have the balls to just do it that way."
He smiles and sits up straighter on the sofa, funnybone connected to the backbone.
• American Pie: Reunion is out in the UK on 2 May
• This article was amended on 8 May 2012. A word was removed as being inconsistent with Guardian editorial guidelines.
