I would like to answer that. I've been involved in several cases involving in-transit shipments coming from China or other countries through Canada into the United States.
On cases I've personally been involved in, counterfeiters have shipped by boat goods originating in China, goods that were stopping in places in Europe and then being offloaded in Halifax to be transported by rail across the country—true cases. Counterfeits are coming in through the FedEx facility in Anchorage and being transshipped through Canada and then back into the United States.
The largest case of counterfeit cellular products, including dangerous batteries and chargers, was a result of an in-transit shipment that would have come through Canada and back into the United States, and it was caught by the combination of customs in the United States and in Canada.
So there is some sort of cooperation; perhaps there were other crimes going on with that shipment such that they caught it. But in transit is something that absolutely happens on a regular basis, where there is cooperation and there is counterfeiting.