54,000 containers left Montreal last month.
That's like 1,800 a day. Say it takes one hour to open a container, investigate it sufficiently without disturbing the contents, then that's 225 working days of investigation every day.
Assuming the port has the infrastructure to allow that kind of investigation, they'd need like 300 employees to do that work.
EDIT: that would probably work out to 30-50 million in personnel, support, and infrastructure costs annually. They'd probably need to pay a bunch more money to retrofit those facilities into the port.
Would it be worth it? Maybe. But nobody wants to foot that bill.