Does fairness flip at the US-Canadian border? Listening to the tax debates going on in both countries, one might think so. In the name of helping the “middle class,” they are considering diverging paths.

In Canada, Prime Minister Justin Trudeau wants to crack down on the tax advantages available to upper-middle-income earners. In the United States, President Trump wants to expand them.

Of course, Canada and the US have different tax structures and different administrations in charge. But there’s something deeper, too. In his book, “Dream Hoarders,” Richard Reeves argues that the real class divide in America is between the upper-middle class and everyone else. The 1 percent aren’t the issue, he says. It’s the top 20 percent who are pulling away.

And that appears to be where the US and Canada are diverging. To Mr. Trudeau, this group is part of “a privileged few.” To Mr. Trump, they’re part of “the middle class” that he says will benefit from his plan.

“Who is middle class?” How each country answers that question will define its sense of identity and prosperity.