She said the two countries held "shared values" ahead of meeting Canadian Prime Minister Justin Trudeau.

Mrs May is also expected to raise a trade dispute that could threaten aerospace jobs in Northern Ireland.

She has previously lobbied US president Donald Trump about the row involving Canadian firm Bombardier, which employs 4,500 people in Belfast, and Boeing.

Boeing has complained about alleged anti-competitive practices in the sale of Bombardier's CSeries jet - and Bombardier could face significant financial penalties if the US trade authorities find against it.

Mrs May's visit comes ahead of a deal between Canada and the EU, the Comprehensive Economic and Trade Agreement (Ceta), coming into force on 21 September.

The PM hopes to use Ceta as the model for a bilateral trade deal for when the UK is excluded from Ceta after Brexit.

Under the EU-Canada agreement, which took seven years to negotiate, Canada agreed to eliminate 98% of its import duties.

Mrs May and Mr Trudeau are expected to set up a new joint working group to prepare the groundwork for a separate deal.

'Shared values'

Under EU membership rules, the UK is prohibited from implementing a foreign free trade agreement until it leaves, so has instead set up working groups abroad, including with Japan, the US and Australia.

Speaking ahead of her visit, Mrs May said: "When we come together and work as one to project our shared values on the world stage, we form a powerful union.

"My visit to Canada today is not only about recognising our past but also looking ahead to our bright future."

She pointed to a "long shared history" between the two countries, adding: "We celebrate together our shared monarchy, and close ties of family and friendship."

The UK-Canada bilateral trade relationship is thought to be worth £15.2bn a year, while Britain is the second-biggest destination for Canadian investment abroad, with £1.75bn invested in the country since March.