Harper has said he will seek assurances that the "Buy American" clause in the $787bn US economic recovery package Obama signed this week will not discriminate against companies in Canada, which sends about 75 per cent of its merchandise exports to the United States.
"This is a huge risk to the world right now. If there is one thing that could turn a recession into a depression, it is protectionist measures across the world," Harper told CNN in an interview.
The "Buy American" provision imposes a requirement that any public works project funded by the stimulus package use only iron, steel and other goods made in the United States.
Harper said he was encouraged by Obama's signals on the issue, but cautioned that Canada had options of recourse under international trade law if necessary.
US officials said Obama would seek to allay Canadian fears.
In an interview with the Canadian Broadcasting Corporation this week, Obama said Canadians should not be concerned, noting that history showed that "beggar thy neighbour" protectionist policies could backfire.
While Obama has stressed that the United States will comply with its international free trade obligations, Harper said last week he was still concerned about the language.
Obama, who wants the United States to take the lead in the fight against climate change, will also discuss clean energy technology with Harper, US officials said, while stressing the importance of Canada as a key US energy supplier.
In his CBC interview, Obama said he wanted to work with Canada on new technologies to capture greenhouse gases, a statement analysts interpreted as recognition that the United States cannot afford to adopt a tougher stance right now against its main energy supplier.
Obama said he would also discuss Canada's role in Afghanistan, where it has 2,700 soldiers as part of a NATO-led force tackling a worsening insurgency. Obama ordered 17,000 more troops there this week.
But Canada, which lost more than 100 troops in the country since 2001, is due to withdraw its troops in 2011.