DETROIT - The battle over a second bridge linking Windsor, Ont., to Detroit saw the Harper Conservatives dispatch a key cabinet minister Monday to give the Motor City the hard sell on the project.

The pitch from Transport and Infrastructure Minister John Baird came ahead of a June 1 vote in the Michigan legislature to adopt or reject the project, and just weeks after Ottawa offered to lend the financially strapped state US$550 million to speed up construction.

"Let's be clear, this is one of the most important projects for enhancing trade in our history -- on both sides of the border," Baird told a lunch-hour audience of Detroit business leaders.

"I'm confident the Michigan legislature will make the right choice."

Baird's visit also came amid a battle with the company that runs the existing bridge crossing, the Ambassador Bridge. Detroit International Bridge Co. has vowed to sue Canada under NAFTA, claiming Canada is trying to undermine it by coercing Michigan into building a new, competing span.

Matthew Moroun, vice-chairman of the parent company of Detroit International, said his company could build a second span to eventually replace the 80-year-old bridge -- using its own money.

"We don't need taxpayer dollars," Moroun told a news conference Monday following Baird's speech. "All we need is for folks like (Baird) to get out of our way and let us complete the bridge."

The U.S. company has said a new span would siphon off traffic from the Ambassador Bridge and bankrupt the firm.

"Most likely the tolls would go up," Moroun said.

"The traffic would be split in half, the expenses of the Ambassador Bridge and the expenses of the new bridge would probably be very redundant and taxpayers would have to come in and subsidize (the new) bridge and we would do our best not to go bust."

The Canadian government says 8,000 trucks and 68,000 travellers cross at the Windsor-Detroit border point daily, along with $130 billion a year in trade.

"I'm here to say that his bridge needs to be built. This bridge must be built," Baird said.

"Working together, this bridge will be built."

Moroun disputed predictions cited by Baird that truck traffic will triple, and vehicle traffic more than double within 30 years.

The project to build a second bridge is expected to create 10,000 construction jobs over five years and 25,000 permanent jobs once it is complete.

The current automotive links between Windsor and Detroit -- a tunnel and the bridge -- together constitute the busiest international border crossing in North America by trade volume.

More than a quarter of all merchandise trade between the United States and Canada crosses the Ambassador Bridge alone.