The Quebec-based company said the contract is expected to be finalized after the SNC-Lavalin consortium building the bridge signs a formal agreement with the federal government this summer.
The value of the contract wasn't disclosed Thursday but Canam said it will be larger than the $200 million deal it signed in November to build the NFL Atlanta Falcons stadium.
The contract announced before markets closed caused Canam's (TSX:CAM) stock to gain 48 cents or 3.44 per cent to $14.43 in trading on the Toronto Stock Exchange.
The new 3.4-km bridge spanning the St. Lawrence River is scheduled to open in 2018.
Canam CEO Marc Dutil has estimated that up to 45,000 tonnes of steel would be needed to complete the structure.
The bridge estimated to cost between $3 billion and $5 billion would have six lanes for cars, two lanes able to accommodate a light rail transit system and a pathway for pedestrians and cyclists.
Canam is North America's largest fabricator of steel components and has worked on several large bridge and stadium projects in Canada and the United States. It operates 22 plants throughout North America, four of which specialize in the fabrication of bridge components.