Trump has for weeks put a circle around April 2 as a "Liberation Day" to impose an array of new tariffs that could upend the global trade system but has provided few details.
He said on Sunday that reciprocal tariffs will target all countries that impose duties on US goods, and the White House said on Monday that any country that has treated the US unfairly should expect to receive a tariff.
Trump also says a 25 per cent tariff on car imports will take effect on April 3.
Trump is due to unveil his tariff plan at an event in the Rose Garden at 4pm on Wednesday (7am AEDT on Thursday).
White House officials say no final decision has been made about the size, scope and target of the tariffs.
According to the Washington Post, aides are considering a plan that would raise duties on products by about 20 per cent from nearly every country, rather than the more targeted approaches that have also been considered.
The administration anticipates the new duties could raise more than $US6 trillion ($A9.6 trillion) in revenue that could be sent on to US citizens as a rebate, the paper reported.
A White House aide said any report ahead of tomorrow's event is "mere speculation".
The Republican president has already imposed tariffs on aluminium and steel imports and has increased duties on all goods from China, raising tensions with the country's largest trading partners.
Canada has vowed to respond with tariffs of its own.
"We will not disadvantage Canadian producers and Canadian workers relative to American workers," Prime Minister Mark Carney said in Winnipeg.
US companies say a "Buy Canadian" movement is already making it harder for their products to reach that country's shelves.
Other countries have threatened countermeasures as well.
Trump has argued that US workers and manufacturers have been hurt over the past decades by free-trade deals that have lowered barriers to global commerce and fuelled the growth of a $US3 trillion US market for imported goods.
The explosion of imports has come with what Trump sees as a glaring downside: massively imbalanced trade between the US and the world, with a goods trade deficit that exceeds $US1.2 trillion.
Economists warn his remedy - hefty tariffs - would raise prices at home and abroad and hammer the global economy.
A 20 per cent tariff on top of those already imposed would cost the average US household at least $US3400, according to the Yale University Budget Lab.
Signs are already emerging that the US economy is losing momentum due in part to uncertainty fostered by Trump's chaotic approach to economic policy making.
A raft of business and household surveys have shown sagging confidence in the economic outlook, citing worries that Trump's tariffs will lead to resurgent inflation.
Factories around the world, from Japan to the United Kingdom to the United States, have had an activity slump in March as businesses braced for Trump's tariffs although some registered a bounce in the race to get goods to consumers before the new measures hit.
Economists say any increase is likely to be temporary.
"It won't be long before US tariffs turn from being a tailwind to being a drag," said Julian Evans-Pritchard of Capital Economics.
