I know this US ambassador is an a-hole, and he tends to shoot his mouth like Trump. However. After reading the article, it isn't as bad as the headline implies. Sending their jets isn't as a threat, but what the ambassador is saying is that more F-35s are needed to fill in whatever security roles it plays in their defensive strategy if Canada buys something else. In the event of some other jets we're using, they would have to alter NORAD in order to allow more US F-35 jets to patrol the skies over Canada.