Looking relaxed in the Ottawa sunshine, the King took part in a tree-planting ceremony, receiving an enthusiastic reception from onlookers, who cheered and crowded round to shake hands with him.
“Canada feels threatened and scared. It is very important he is here,” said Theresa McKnight, from Mississauga, Ontario.
Her sister Dianne St Louis from near Toronto agreed: “It’s critical. It means a great deal to have the King standing side by side with Canadians.”
There had been a warm welcome at Ottawa airport, for what will be a visit of about 24 hours on the ground in Canada.
Carney was on the runway to meet the royal visitors, with a welcoming party that included schoolchildren from English- and French-speaking schools and representatives of First Nations communities.
A community event had also been a checklist of Canadian moments, such as the King dropping a puck to start a game of street hockey and getting jars of maple syrup.
But the main focus of this trip will be the historic speech on Tuesday, with the prospect of the King delivering the Canadian government’s message of rejecting calls to become the US 51st state.
It is also a diplomatic balancing act because in his role as head of state of the UK, the King has been part of an effort to keep good relations with Trump, including inviting him for a second state visit.
But in Canada, the King will have to speak on behalf of Canada. As another bystander said at Rideau Hall: “Sovereignty is important and he is the epitome of that.”