Harper's comments came as he announced an agreement to construct a $1-billion link between Windsor, Ont., and Detroit.
"This new bridge, the second across the Detroit River, is an investment in the future — in the future of the North American economy, in North American trade and North American manufacturing," he said.
"This is the most important piece of national and international infrastructure that this government will complete while I am prime minister," he said.
Under terms of an agreement in principle with Michigan, Canada is financing the construction, and will recover the state's share of the cost through tolls on the American side of the Detroit River.
The addition of custom plazas and highways — coupled with the costs of land expropriation — will see the total bill swell to $3.5 to $4 billion.
The work is also expected to create thousands of jobs on both sides of the border.
The new span will be a few kilometres south of the existing Ambassador Bridge, which has become a serious bottleneck for trucks moving between the two countries.
Canada, the U.S., auto makers and other industries have argued for years that another crossing is desperately needed to end truck gridlock and provide an alternative if the existing bridge is shut down in the event of a terrorist attack.
Harper was joined for the announcement, ahead of a formal signing ceremony Friday in Detroit, by Michigan Gov. Rick Snyder, who said his state simply didn't have the resources to proceed without Canada's help.
Snyder said his government is learning from Canada's example on how to pull off this kind of public-private partnership.
"We actually have embraced a number of good thoughts and ideas that came from the Canadians on how they're doing projects in this country," he said.
Later in Detroit, two groups of demonstrators — for and against the project — shouted each other down across from where the signing ceremony was taking place.
The project has faced stiff resistance from Manuel (Matty) Maroun, the billionaire owner of the Ambassador Bridge.
Maroun has publicly decried the new project as an unnecessary boondoggle and some reports suggest he would launch a lawsuit in an effort to block its construction.
Harper said the Michigan and Canadian governments anticipate some fights but the need for the link is overwhelming.
“We should make no mistakes," he said, "Whatever battles lie ahead this bridge is going to be done."
Michigan's Republican-controlled state legislature rejected the bridge project last year, forcing Snyder to work out the deal that doesn't involve spending of Michigan tax dollars.
The Ontario government has also called the project critical to the province's economy and Premier Dalton McGuinty was on hand for the announcement to thank Harper and Snyder.
John Manley, CEO of the Canadian Council of Chief Executives, praised the agreement.
"(The) announcement of the planned construction of a second bridge is a major step forward for our bilateral trading relationship, and will mean faster, more reliable border crossings," Manley said.
"This much-anticipated second bridge will help companies that rely on just-in-time production to keep costs down and improve their competitiveness."
The Canadian Trucking Alliance also gave the project a "huge thumbs up."
Alliance president David Bradley said years of political wrangling had delayed progress on a second crossing.
"The need for a new bridge — in terms of both the economic viability and long-term security of both nations — is pretty self-evident."
It's not clear when the actual construction might start and it is at least five years from completion. Among other things, expropriation of land on the U.S. side still has to take place.