Their car was headed into Canada when it was directed into a secondary inspection area - and that's when a suspicious package was discovered by the Canadian Border Service Agency.
It happened at 5 p.m. and Windsor police's bomb squad arrived about an hour later.
The suspicious package that everyone on edge was commercial grade fireworks and brass knuckles. The smoke grenade could be used as an incendiary device, police say.
The men were driving a Michigan-plated vehicle with two occupants from Michigan inside, police say. Charges are pending for both suspects and no further descriptions - other than they are both young men - was given.
The security scare caused a big headache for people wanting to get to Detroit and those headed back to Canada.
People like Jay Verspeelt, a reporter for the Urbanite news.
"Debating whether I should stay on the bus or go grab a drink," he said. "I'm just waiting to get back across the river."
Canadians who took the tunnel bus service to Detroit were stranded in the motor city for hours.
Then, a rescue mission of sorts - Windsor Transit sent buses over the Ambassador Bridge and picked up hundreds of Canadians
By 9 p.m. the tunnel was reopened.
"We heard there was almost 400 stuck at the auto show," said a bus driver picking up stranded Canadians.