And they will be in no doubt: Trump is trouble.
He is trouble for their economies, politically toxic in their respective countries, and takes up an inordinate amount of their valuable time and energy.
For beauty and tranquility, the setting of this year's G7, the Manoir Richelieu hotel in the spectacular Charlevoix region of Quebec, rivals that of last year's location, the old Sicilian coastal town of Taormina, Italy.
Tensions have been mounting ahead of what could be a watershed summit that comes to define a new relationship between America and the other big trading nations.
The host prime minister, Canada's Justin Trudeau, is incensed by Trump's decision to impose trade tariffs
on the grounds of "national security.".
China fears that, whatever Trump's negotiators say, the President may yet choose to spark a trade war with Beijing.
EU leaders are not only seething about the Trump tariffs
, but are also smarting about his decision to pull out of the Iran deal, which could result in European businesses being hit with secondary sanctions.
As for Japan, go ask PM Shinzo Abe what he thinks
about the impending summit between Trump and North Korean leader Kim Jong Un. He's likely to make his displeasure clear again to Trump in person on the eve of the G7 as well as at the summit proper.
France's Bruno Le Maire
described the preparatory summit of finance ministers as "more of a G6+1, with the USA alone against everyone."
No one thinks Quebec will be any different.
In Taormina last summer, Trump began to show what he'd be like in a room full of world leaders. Trump appeared unprepared, refusing to take a decision and join other leaders in backing the 2015 Paris global climate agreement
Italy's PM, Paolo Gentiloni, the host, rebuked him, calling for "professionalism" at the negotiating table.
A few weeks later, Trump pulled out of the Paris accord altogether.
Nevertheless, relations didn't fall apart immediately. After all, days earlier, Trump had backed away from calling NATO "obsolete", as he had done during his election campaign.
On a visit to NATO's new HQ in Brussels, he complained about the cost of the building, but after hectoring the leaders on why they should pay their way
, he agreed to do business with them after all.
Flush with his own recent electoral triumph, France's youthful President Emmanuel Macron, custodian of the Paris Climate accord, began a high-profile "bromance"
He lavished honors on the first couple, courted them with dinner with him and his wife at a Michelin-starred restaurant in the Eiffel Tower, and the coup de grace, ringside seats for France's thunderous Bastille Day celebrations, including a full military parade that so impressed Trump he demanded one of his own in DC.
Yet here we are less than a year later, on the brink of perhaps the most strained G7 in recent years.
Macron's Trump "Bromance" is apparently over, victim of trade and other tensions and whatever kind of shade the pair threw at each other in a phone call last week. By all accounts, Trump didn't take Macron's criticism well.
So how will he hold up in Quebec, and how will the other leaders handle him?
Early indications are not good.
Within days of Trump's inauguration last year German Chancellor Angela Merkel began calling on EU leaders to take control of their destiny. She re-upped that call following Trump's unilateral withdrawal from the six-nation Iran deal, the JCPOA.
China has warned Trump that if he reneges on trade commitments made by his negotiators, all bets are off.
In short, in the absence of common ground with Trump or at the very least consistency from him, leaders will be more likely to follow their own national security interests to head off damage from his "America first" policies.
Not only is this antithetical to the G7 concept of collective trust and problem sharing, it leaves the world more brittle and prone to fracture along fault lines that generations of leaders have struggled to prevent since the end of the Second World War.
Even Trump's most hopeful and needy European partner, Britain's embattled PM Theresa May, is reaching the end of her patience.
In a phone call earlier this week, she told Trump that the decision by the US to apply tariffs to steel and aluminum imports from the EU was "unjustified and deeply disappointing."
In barely a month's time, May is due to host Trump on a visit to the UK, where thousands of anti-Trump protestors are expected to take the streets.
Last year 1.8 million Brits signed a petition
calling on the PM to rescind the invitation she made less than a week after his inauguration.
The latitude May and other leaders at the G7 have to let Trump be Trump has dried up.
At summits like this, disagreements typically manifest themselves in the brevity of the final communique.
The more the leaders have disagreed, the shorter the final statement.
But even the most experienced government officials will have trouble burying this scale of trouble under a few carefully crafted lines of diplomatic niceties.
There just isn't a diplomatic carpet big enough to conceal all the mess that needs to be swept under it.
Correction: An earlier version of this article incorrectly indicated China is one of the G7 nations.