OTTAWA -- A new connection in the trading relationship between Canada and the United States will cost $5.7 billion, with one senior official vowing the Gordie Howe bridge will elbow its way through any legal or political challenges --including from U.S. President Donald Trump himself.

Construction of the long-sought span named for the Saskatchewan-born Howe, who became a hockey legend while playing for the Detroit Red Wings, will begin this fall at Canada's busiest border crossing and take six years to complete.

Getting to Friday's announcement of the final price tag for the span over the river between Windsor, Ont. and Detroit, has been laden with political potholes that proponents have had to navigate at the state and federal levels.

The bridge has also survived multiple legal challenges from the private owner of the nearby Ambassador Bridge, who publicly appealed to Trump this year to revoke a presidential permit Barack Obama granted to greenlight construction.

Dwight Duncan, the chairman of the federal agency in charge of the bridge, said proponents have set in place the political infrastructure to ensure the project survives a change in Michigan's state government or trade disputes between the two countries.

"Vice President (Mike) Pence, when he was governor of Indiana, was a huge supporter. A range of Trump's top supporters in the state of Michigan have urged that he continue on with this project. So I'm confident that regardless of what other issues our two countries are dealing with, this project is going ahead," Duncan said.

"We're going to get this thing built."

The six-lane, 2.5-kilometre cable-stayed bridge -- whose towers will be designed to look like a hockey stick taking a slap shot -- won't open to traffic until the end of 2024. It will have a lifespan of 125 years.

About one-quarter of all goods traded annually between Canada and the U.S. passes through the Detroit-Windsor corridor.

How much the bridge would cost has steadily increased since the previous Conservative government found a way to bypass American lawmakers and a funding stalemate that threatened to thwart the long-discussed project.

The contract unveiled Friday with a private construction consortium largely sets the final price: $3.8 billion to design and build the span, as well as $1.9 billion more to operate and maintain the bridge and its ports of entry on both sides of the border for 30 years.

Labour disruptions and additional environmental work are among the risks that could drive up costs, but the construction consortium will have to swallow any increases in labour or materials costs. Federal officials could also withhold payments if construction timelines slip.

The major risk for the bridge authority is that the project doesn't earn enough from user tolls to cover the federal investment, although the authority believes observed increases in commercial truck traffic will continue.

The Liberals were told about potential cost increases in the project shortly after coming to office, and former infrastructure minister Amarjeet Sohi ordered the bridge authority to find some cost savings -- but officials wouldn't discuss the details of the review on Friday.

Duncan said an outside review suggested the final price would have been more than $6.2 billion if the Canadian government had decided not to partner with a private-sector consortium and foot the entire bill itself.

"There is terrific value for money for Canadian taxpayers who are financing this and ultimately for users of the new border crossing who will be paying the tolls that will pay back the Canadian government," he said.

Work to build the bridge will have to account for tricky environmental conditions, such as ground that needs to settle to support the pillars holding up the span.

The ports of entry on both sides of the crossing will be among the largest in North America, and will include green space and Indigenous art on the Canadian side.