Britain's King Charles III arrived in Ottawa Monday for a visit to open Canada's parliament, a brief trip seen as part of the pushback against US President Donald Trump's annexation threats.

The 76-year-old monarch, who is Canada's head of state, was greeted at the airport by Prime Minister Mark Carney, who has invited him to give an address opening Canada's new legislature.

The so-called throne speech outlining the government's priorities is typically given by the British monarch's representative in Canada, the governor general.

Queen Elizabeth II, the king's late mother, delivered a throne speech in Canada just twice during her long reign, in 1957 and 1977.

Charles, making his first visit to Canada since his coronation, will be closely watched for any comments on Canada's sovereignty, and on trade.

Trump has slapped tariffs on Canadian goods including sector-specific levies on autos, steel and aluminium, rattling the Canadian economy, although he has suspended some of them pending negotiations.

Carney has said his newly-elected government has been given a mandate "to define a new economic and security relationship with the United States," a neighbour he believes Canada "can no longer trust."

He has promised to curb reliance on trade with the United States by boosting internal commerce while forging deeper economic ties with allies overseas.

The government's path to build up Canada and create new relationships will be outlined in Charles's speech, Carney said Monday.

"This historic honour matches the weight of our times," he said in a statement.

A government statement described the visit as "a momentous and historic occasion that underscores Canada's identity and sovereignty as a constitutional monarchy". (Reuters)