They would want something in return. They are bargaining chips. What they would probably
want would involve something that didn't conform to the treaty on FM. It would probably be way out of proportion to relinquishing the AM frequency. It would probably involve interference to a US station, or relinquishing an FM frequency of a US station to Canada. It's like some human relationships, and international relations at some much higher level than an AM or FM frequency. That said, there are usually ways around it. And to be fair, there are US stations who want large concessions, out of proportion to the value of the station, to accommodate an upgrade.
DLR initially proposed deletion of 1160. IT WAS A VACANT ALLOTMENT, NOT A STATION. There is now an 1170 allotted to Thunder Bay. What happened in between isn't clear. Maybe it's in a later application. It was alluded to as "in another part of the application" in the original application.
On the US side, they upgraded WHBY 1150 Kimberly, WI.