King Charles III will deliver a significant speech in Canada's parliament later on Tuesday that is expected to offer his support in the country's dispute with US President Donald Trump.

The King and Queen Camilla received a warm welcome when they arrived in Ottawa, on the royal couple's first trip to Canada since the start of their reign.

Soon after arriving, the King, who is Canada's head of state, held a meeting with Prime Minister Mark Carney, recently elected on a wave of anti-Trump public opinion.

Carney has praised the "historic ties" that make up Canada's independent identity, including the "vitality of our constitutional monarchy", which he said "crises only fortify".

Carney invited the King to deliver the speech at the opening of parliament after his recent general election victory, in a campaign dominated by the threats to Canada's sovereignty from Trump.

It will be the first time in almost 50 years that a monarch gives the Speech from the Throne, with the King's decision to come to parliament in Ottawa seen as a symbolic show of support for Canada.

The King's speech will be written on the advice of the Canadian government, with the expectation that it will send a clear, if diplomatic, message that the country is "not for sale" to the US.

Carney said in advance that the speech, to be delivered in French and English, would match "the weight of our times".

On Monday afternoon, the King and Carney held a meeting at Rideau Hall, the residence of Canada's governor-general, with both men sitting in front of Canadian flags.

There were also meetings with leaders of Canada's indigenous and First Nations groups, including Cindy Woodhouse, the national chief of the Assembly of First Nations.

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."