Exactly, if it wasn't important to them they wouldn't have mentioned anything.  Sometimes the best defense is a good offence.  

Cancel the coal imports for shipping to China and watch the U.S. take notice quickly.  The time it takes to set up the logistics to re-route through American ports will cause a big issue and likely impact the short-term profits in coal mining industry.  The added expense to fixed cost contracts should cause long-term impact to profits to an influential part of Trump's base.

The very best thing we can do is not to be push overs.  Whether Trump likes it, or not, a large part of the US depends on easy access to Canadian goods and services.