I think Canada's position is strong legally, that these are internal waters. I think we've built it up effectively over a long time. It was almost an étapiste, step-by-step approach to doing it.
We weren't bold; we didn't come out of the gates when people were talking about it in 1946. In that sense, I think the U.S. could in theory do that. There are a whole bunch of eminently practical reasons why it wouldn't be in the U.S. grand strategic interest to push it.
So it's possible, but improbable.