Donald Trump will fly headlong into a confrontation with some of America's closest allies today, as the row over tariffs and fears of a trade war continue to intensify.
Prime Minister Theresa May is among the G7 leaders who have criticised the US president for not exempting the EU and Canada from his new tariffs on steel and aluminium imports.
The summit has already been dubbed the "G6 plus one" due to Mr Trump's isolation over trade and his decision to pull the US out of the Iran nuclear deal.
These summits are usually seen as a cheerful and informal demonstration of shared purpose and responsibility among the world's richest economies.
But some of those who Mr Trump will join for two days of talks at a luxury castle in the Canadian mountains have already abandoned the tradition of playing nice in public, whatever the differences behind the scenes.
French president Emmanuel Macron, who describes Mr Trump as a "friend", has taken a more confrontational approach ahead of the summit.
He told reporters: "Maybe the American president doesn't care about being isolated today, but we don't mind being six, if needs be.
"Because these six represent values, represent an economic market, and more than anything, represent a real force at the international level today."
In what's been seen a jab at Mr Trump, he added: "Nobody is forever."
Mr Macron was speaking alongside Canadian prime minister Justin Trudeau, who is hosting the summit, and the pair signalled they would warn Mr Trump of the potential damage tariffs could cause the US.
Mr Trudeau said: "American jobs are on the line because of his actions and because of his administration.
"When we can underscore and we see there's a lot of pressure with the US, perhaps he will revise his position."
Few though expect Mr Trump to back down, prompting fears of a bad-tempered summit and the prospect of leaders not agreeing the traditional end-of-summit communique.
Mr Trudeau has described the US claim that the tariff decision was taken on national security grounds as "insulting". It is been reported that, in a phone call between the two leaders, Mr Trump wrongly accused Canada of "burning down the White House in 1812" as partial justification.
It has also been suggested that Mr Trump had not been keen to attend the summit at all, with expected criticism and his meeting with North Korean leader Kim Jong Un looming.
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Before departing for Canada, Mr Trump tweeted: "Please tell Prime Minister Trudeau and President Macron that they are charging the US massive tariffs and create a non-monetary barriers. The EU trade surplus with the US is $151bn, and Canada keeps a farmers and others out. Look forward to seeing them tomorrow."
He claims the US has long been the loser in international trade and that he is determined the right the balance, starting with the tariffs.
Mr Trump's top economic adviser Larry Kudlow says other are counties are to blame for the current situation because they have taken advantage of the US.
"Don't blame Mr Trump, blame the nations that have broken away.
"The global trade system is broken and President Trump is trying to fix it. That's the key point."
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Mr Kudlow described the discontent among US allies as being like a "family quarrel" but said that the White House was confident that talks would bring a solution.
The G7 - or group of seven - comprises the largest advanced economies in the world: the UK, US, Canada, France, Germany, Japan and Italy. It returned to its original make-up after Russia was expelled from the-then G8 over the annexation of Crimea in 2014.
This year, if members can overcome their differences on trade and Iran, the summit offers some scope for unity on issues such as girls' education, gender violence and chemical weapons.
Canada has made ridding the world's oceans of plastic pollution a signature issue and it is a central theme of the summit.
But this year's talk of tackling climate change will be a reminder of the divisions that have widened in the G7 family.
At last year's summit in Sicily, Mr Trump would not agree to sign a closing statement on climate change and withdrew the US from the Paris agreement days later.