Obama's comments followed speculation ahead of his visit that he was likely to request a greater contribution to US-led forces battling the Taliban in Afghanistan, as Robert Gates, the US defence secretary, asked Nato allies meeting in Poland for extra troops.
Al Jazeera's Nick Spicer, reporting from Ottawa, said public sentiment in Canada has long been against further involvement in Afghanistan and many questions had been asked over whether Obama would request an extension to Canada's troop presence there.
Obama was greeted by a cheering crowd of around 1,000 people as he arrived at Parliament Hill in Ottawa for talks with Harper.
'Buy American' concerns
The US leader also played down any concerns over economic protectionism after signing his $787bn stimulus package into law this week.
The stimulus plan includes a "Buy American" clause that has sparked controversy in Canada, the United States' largest trade partner and major source of energy.
|Obama, left, and Harper also discussed the economy and the environment [Reuters]
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 US.
Obama said he gave assurances that his administration wanted to "grow'' trade with Canada, and not contract it.
However, Harper reiterated that such economic stimulus plans which benefit "ourselves [the US] ... at the expense of others ... will deepen the world recession, not solve it".
Both leaders also said they were "deeply concerned" about the current state of the North American car industry, with Obama saying that it faced "significant restructuring" due to the economic crisis.
US car giants General Motors and Chrysler announced they would shed 50,000 jobs this week as the companies struggle to overcome slumping demand and the financial crisis.
Obama and Harper also said they discussed security concerns over their shared border and hailed an agreement between the two men to begin a clean-energy dialogue aimed at dealing with the greenhouse gases that are blamed for climate change.