LONDON/OTTAWA - King Charles flies to Canada on Monday for a highly symbolic visit showing support for the nation that recognises him as its sovereign but is coveted by US President Donald Trump as a 51st US state.

Following an invitation from Prime Minister Mark Carney, Charles will open parliament in Ottawa on Tuesday, the first time a British monarch has carried out the duty since his mother, the late Queen Elizabeth, did so 68 years ago.

The 76-year-old king is still undergoing cancer treatment, which has limited his workload, so the two-day trip shows his commitment to Canada, one of 15 countries where he is monarch.

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Trump has repeatedly expressed a desire to annex Canada, a proposition fiercely rebuffed by Carney whose election win last month came partly on the back of that stance.

"The prime minister has made it clear that Canada is not for sale now, is not for sale ever," Canada's envoy to the UK, Ralph Goodale, told reporters during a visit last week by Charles to Canada's high commission.

"The king, as head of state, will reinforce the power and the strength of that message."

Charles has made subtle signals of his backing for Canada in recent months, wearing Canadian medals, calling himself the king of Canada, and describing its flag as "a symbol that never fails to elicit a sense of pride and admiration".

However, he faces a tricky balancing act as British Prime Minister Keir Starmer is working to keep Trump onside over Ukraine and trade ties.

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When Starmer visited the White House in February he made great show of an invite from Charles for an unprecedented second state visit for Trump, whose mother was born in Britain and who has repeatedly praised the British royal family.

Carney, the former governor of the Bank of England, said that had irked Canadians.

'Momentous occasion'

Charles' trip, which he will make with his wife Queen Camilla, will be his first visit to the former British colony since becoming king in September 2022.

On Monday, the royal couple will visit a large park in Ottawa and meet vendors and artists, according to Buckingham Palace. The king will then participate in a ceremonial puck drop to launch a street hockey demonstration before planting a tree in another part of the city.

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It will be just the third time a sovereign has delivered a "Speech from the Throne" in the Canadian Senate, an event which opens every new session of parliament.

Charles and Camilla will travel to the Senate in a ceremonial horse-drawn carriage with a 28-horse escort to deliver a 25-minute speech written by Carney's government.

Canadian Identity and Culture Minister Steven Guilbeault said it would be a "momentous occasion - one that brings Canadians together in celebration of our rich history, our democracy and the institutions that serve us all."