Prime Minister Theresa May has said she will press President Trump on the US trade dispute that could threaten jobs at Bombardier in Belfast.
Bombardier, a Canadian aerospace firm, is Northern Ireland's largest manufacturing employer.
Rival firm Boeing has complained about alleged anti-competitive practices in the sale of Bombardier's C-Series jet.
Mrs May was speaking in Ottawa after talks with Canadian Prime Minister Justin Trudeau.
"I will be impressing on [Mr Trump] the significance of Bombardier to the United Kingdom and particularly... to jobs in Northern Ireland," she said.
Mr Trudeau renewed his threat to cancel an order with Boeing for 18 Super Hornet fighter jets.
He said: "We won't do business with a company that's suing us."
In 2016, Bombardier won its biggest ever order to provide its C-Series passenger plane to Delta, a major US airline.
Boeing has alleged that Bombardier engaged in "price dumping" by agreeing to sell 75 of their planes for almost $14m (£10.6m) below their cost price.
It said Bombardier can only afford to do that because of financial help that it has received from the Canadian and British governments.
It wants the US government to hit Bombardier with punitive tariffs.
The UK and Canadian government have been trying to pressure Boeing to withdraw its complaint.
Last week, it emerged that Mrs May had discussed the issue in a phone call with President Trump.
But on Monday, Boeing issued a statement restating its position.
It said: "No-one is saying Bombardier cannot sell its aircraft anywhere in the world.
"But sales must be according to globally-accepted trade law. We all have a shared interest in a level playing field. That is what this dispute is about."
Bombardier has described Boeing's allegations as "absurd".
It said any government support "complies with the laws and regulations in the jurisdictions where we do business".