On Thursday, Trump - during a hastily arranged meeting that caught his staff and entire administration off guard - told reporters he will slap a "25 percent" tariff "for steel" imports and a "10 percent for aluminum".
In B.C., it's unsure at this point how the proposed US government's 10 per cent tariff on aluminium imported into the USA would impact Rio Tinto's BC Works in Kitimat.
A senior USA official said the measures would take effect about two weeks after Trump signs the proclamation.
"Of primary concern to us is uncertainty around the trade and investment climate leading to a shortfall of capital flow into Canada", said Ben Randol, senior FX strategist at Bank of America Merrill Lynch.
The European Union (EU) and China are considering retaliatory measures.
Gov. Kim Reynolds expressed concern Monday that President Donald Trump's tough talk on imposing trade tariffs could stunt Iowa's economic potential if other countries take retaliatory measures against US farm exports.
"Trade wars are never won".
"If we're able to make a deal with Canada and Mexico in NAFTA, then there will be no reason to do the tariffs with Canada and Mexico", he said.
The President later tweeted: "To protect our Country we must protect American Steel!"
Canada and Mexico are exempt from the tariffs, but only conditionally and for now. "Tariffs on steel and aluminium will only come off if new and fair Nafta agreement is signed", Mr Trump tweeted.
"But they try to resolve some of the issues within the sectors to see if they can get some agreement, whereas this nearly gets so, 'Well, if you don't do this, we'll just sacrifice another whole sector, '" he added.
However, he said the deal has benefited the US, which he said has about 9 million jobs that depend on free trade with Canada. Total trade between the countries reached $636 billion previous year, according to United States government data.
Ongoing depreciation of the dollar would make it hard to rein in the trade deficit, which Trump has pledged to shrink.
"The so-called "carve out" of Canadian steel and aluminum tariffs would allow USA trade negotiators to have what a senior administration official described as "ongoing discussions" about various issues between the three countries", CBC reporter Pete Evans writes. It sends 75 percent of its exports to the United States.
The Trump administration launched a Section 232 investigation past year into the impact of imported steel and aluminium on the U.S.' national security.