Posting on his social media platform Truth Social, Trump warned that any such move by Canada would trigger immediate and sweeping trade penalties.
"If Canada makes a deal with China, it will immediately be hit with a 100% tariff against all Canadian goods and products coming into the USA.," Trump wrote.
He referred to Canadian Prime Minister Mark Carney as "governor" and said Carney would be "sorely mistaken" to allow Canada to become a "drop off port" for Chinese products headed to the US market.
Trump also predicted severe consequences for Canada from closer economic ties with Beijing.
"China will eat Canada alive, completely devour it, including the destruction of their businesses, social fabric, and general way of life."
In a later post, Trump said a Chinese takeover of Canada was unacceptable.
"It’s not going to happen, or even come close to happening," he said.
In response, Ottawa rejected the US president’s assertions.
Canada said recent discussions with Beijing were limited in scope and did not involve a broader trade pact.
"There is no pursuit of a free trade deal with China. What was achieved was resolution on several important tariff issues," Dominic LeBlanc, Canada’s minister responsible for Canada-US Trade, said in a statement.
LeBlanc said the Canadian government remains focused on strengthening economic ties with Washington.
He cited Carney’s earlier remarks that Canada and the United States "have built a remarkable partnership in our economy and security."
LeBlanc added that Ottawa is committed to ensuring the relationship benefits "both sides of our border" while strengthening the domestic economy and expanding global trade partnerships.
As tensions escalated, Carney addressed Canadians directly.
Carney urged citizens to support domestic businesses, describing the Canadian economy as “under threat from abroad.”
In a video message, he said his government is pursuing major initiatives, including the construction of millions of homes to improve affordability and the acquisition of military hardware "that will protect Canadians and our sovereignty."
"We can't control what other nations do. We can be our own best customer," he said.
The comments follow recent trade developments between Ottawa and Beijing.
Last week, Canada said it had reached a trade agreement in principle with China after Carney’s visit, easing tariffs on Chinese electric vehicles in exchange for reduced duties on Canadian agricultural exports.
Trump said on Friday that Canada opposes his proposed "Golden Dome" protection over Greenland and had instead "voted in favor of doing business with China."
Relations between Washington and Ottawa have deteriorated sharply since Trump took office last January, as Carney has sought to counter US tariffs while rejecting calls for Canada to become the 51st US state.
In the latest sign of strain, Trump took further action.
Trump withdrew Canada’s invitation on Thursday to join his "Board of Peace," a move seen as retaliation for Carney’s remarks at the World Economic Forum.