i would prefer the good neighbour policy.
however, i actually agree that it's crazy that the united states doesn't have troops on the panama canal. i'm not suggesting they need to go in there and take this guy out like they did noriega, or that they should occupy the whole country, but they should absolutely have a clear presence protecting the canal itself, including a blockade on the north american side to keep migrants south of the canal. it's a choke point.
they could always nuke it and open up the lanes a little (yes i'm joking).
the united states has invaded greenland and iceland before and will do so again if it has to. it's really up to the islanders, not to denmark or norway. if i lived there, i might think about it.