What about the real Sutherland? Does he identify with the story; does it bring home his own mortality? Sutherland is at the Toronto Film Festival, along with Virzi and Mirren, to promote the film. There is a brief, incredulous silence. "I'm 83," he says eventually, by way of reply. As Mirren has already told an interviewer in Toronto, death is part of life; when you're 83, it's inevitably looming large.

"I always say you either die young or get old," she says. "Coming to terms with that is part of the process of life. But you can only understand or realise that as you pass through life yourself."

Even though this is John's tragedy, the story turns on Ella's courage and zest for life; Mirren is correspondingly the linchpin of the ensemble. Both Virzi and Sutherland rush unprompted to say how wonderful she is. Sutherland says he was drawn to Virzi and loved the script, which the director wrote with novelist Stephen Amidon – he was already an admirer of Amidon's – but then they "got Helen. What else can you do? I just love her. I've worked with two brilliant women, really women you could easily say are geniuses: Jennifer Lawrence and Helen."

For his part, Virzi beams just thinking about her. "She arrives on set in the morning usually very cheerful and talking about other things – weather, Italian food – and she becomes Ella in the moment the camera rolls. And she performs flawlessly, leaving us astonished or exhilarated; she is a very witty and smart person, so nice, simpatica, simpatica!"

Virzi is best known outside Italy for his two most recent films. Human Capital (2013) was a coruscating view of a rich family paying its way out of trouble; it was based on a best-selling novel by Amidon but was relocated, surprisingly successfully, from Connecticut to Italy. His next film Like Crazy (2016) starred his wife Micaela Ramazzotti alongside Valeria Bruni Tedeschi as two women who make a break for mad freedom from a psychiatric hospital, stealing a car and driving into the never-never: another getaway movie.

Virzi is also, quite possibly, the most purely delightful person I have ever interviewed. He is 54: grumpy dementia seems a long way off. He is also very Italian. "I know!" he says. "I never expected that some day I would have set a film in a country that is not my own and in a language that is not mine – because my English is not perfect, as you can hear. I was a little scared to miss something of my tools of the trade. It was a risk."

He never felt exactly like a stranger in America, however, because he had grown up with the literature John reads and films that had made the landscapes feel familiar. He is, as he puts it, "a son of the Italian cinema and proud of that", but he also feels he owes a personal debt to Robert Altman and Martin Scorsese, even to the much younger Alexander Payne. "There are so many filmmakers I feel familiar with."

Reverence for American cinema has its own pitfalls, of course. "It was a risk to get stuck in cliche, like it happens to many very good American directors when they come in Italy and shoot against the backdrop of Italy's picturesque places," he says. In Michael Zadoorian's source novel, John and Ella drive Route 66. Virzi baulked at filming in iconic Monument Valley, so relocated the drive to "the languid and sweet landscape" of the East Coast. He hopes he avoided caricaturing the country. "I am awaiting your opinion," he says in Toronto, where it is being unveiled to North America.

Opinions turn out to be mixed. "Although shot entirely in the States, everything feels artificial, from bland images in trailer parks to a hold-up scene that can only be described as inept," wrote the Variety critic – an American who lives in Italy – after describing the story as one of those "Alzheimer's movies that pander to the worst sort of cheaply manipulative old-folks cutesiness". Many critics had exactly the opposite view on both counts; in the Telegraph, another critic admired the way an outsider could spin "a film that's fizzily curious about the state of America right now".

The Leisure Seeker is less about any of this, however, than it is about old love. "It's what happens," says Mirren, "after 'and they lived happily ever after'." And it isn't cute about that; Ella is exasperated beyond endurance much of the time, not least by John's less-than-cute incontinence.

It is a small story, agrees Virzi, but it is pinhole view of a vast subject. "The sense of a life. The meaning of a life. Here is a couple who, in their getaway, bring with them pieces of their memory and obsessions and petty jealousies and this combination of devotion, intolerance and bickering that makes the love real and true."

And it ends with another '70s hit: Janis Joplin singing Me and Bobby McGee. "With the purity of a sweet ballad, we wanted to find a way to sing a hymn to personal freedom and dignity," Virzi says. We watch as these two people who require care, as their children keep reminding them, choose to be carefree. "Life is to be lived in every single moment, even at the end," Virzi concludes. "Especially at the end!" Even when you've lost your marbles.

The Leisure Seeker opens on June 14.