In a forest on the west coast of Canada, two middle-aged British women are lost. Off they trot, straining under the weight of their heavy backpacks, only to come back the same way later on, past the same magnificent trees to try another route. Unmistakably, this is the return of Race Across the World.

Partly a nod to Jules Verne but mainly inspired by the urgent need for humankind to stop flying, Race Across the World sets a simple challenge. Travelling in pairs, contestants must complete an epic trip as quickly as possible, stopping at checkpoints along the way. It was London to Singapore in season one; Mexico City to Ushuaia, Argentina, in season two; and in this new, third run, the whole race takes place in Canada, zigzagging from Vancouver to St John’s. Teams are given money that would have covered the air fare, but they can’t do any of the trip by plane and they can’t access the internet to get tips on making the journey, which means they often have no idea how to proceed.

The resulting spectacle – a messy celebration of human foibles, resilience, diversity, resourcefulness and generosity – is a gameshow, travel show and reality show all in one.

There’s the game itself, where we the viewers at home confidently identify mistakes we definitely wouldn’t have made and better options we certainly would have thought of under pressure. Then there’s the game within a game for the more cynical spectator, which involves guessing to what extent the travellers have made their own choices, and to what extent the producers have nudged them to create an episode with a neat shape.

RATW also serves as a vicarious dream holiday. Among viewers with the means to fly across the world on a jolly, booking inquiries for British Columbia are about to experience a big spike. Tasked with travelling north from Stanley Park, Vancouver to the first checkpoint at Tlell on the Haida Gwaii archipelago, the contestants who travel by ferry see whales, sea lions, bald eagles and stunning islands; those foolish enough to trek over land still enjoy mountain and forest scenery that makes Switzerland look like Stevenage.

For those unfamiliar with the area, the surprise is the mode of travel the participants have to master. It seems British Columbia doesn’t really do public transport. The next bus to where you want to go arrives the day after tomorrow and there isn’t a train. Even those travelling up the only main road on Vancouver Island, to get from one ferry terminal to another – and hurry, because the ferry only goes three times a week! – have to hitch rides in strangers’ cars.

This gives the show a chance to show off one of its many hidden strengths: the ability to find helpful civilians who can be stars for five minutes. Leading them this week is Corey, some dude hanging around outside the Costco in Prince George who would be played in a film by Seth Rogen or, back in the day, John Candy. Corey agrees to be paid C$250 for a 10-hour drive north because he has no other plans, although he would like to stop off and jump in a lake as a tribute to his dead dog. Mobeen and Zainib, a married couple with a delicate relaxed v spiky-energy dynamic, are his passengers. Mobeen jumps in the lake.

The secrets and tensions within relationships, magnified and then inevitably resolved on the journey – a process these people have chosen to undergo in a foreign country, on national television – are what make Race Across the World a top-tier reality show, and this year’s cast could be the best ever. We already have a hint of why brothers Marc and Michael have never been close, and before they’ve reached Tlell, Claudia and her father, Kevin, have revealed exactly why they are so fractious. Ladi and his daughter Monique seem to just have a regular generational clash going on, but maybe there’s more to it.

Early favourites, though, are the pair who got lost in Stanley Park as soon as the race started. Tricia, 48, and Cathie, 49, have been best pals since school, and the way they fit together would make a dramatist purr. Tricia is louder and taller and needs Cathie to keep her grounded; Cathie needs Tricia to go up to customers at petrol stations and beg for a lift. When Tricia tells us why she has to see Canada now, not in a few years’ time, we know the two of them are going to cheer our souls and break our hearts before we all get to Newfoundland.

Race Across the World was on BBC One and is on iPlayer.