If Diane Francis had her way, the U.S. would share a lot more with its northern neighbor than the Great Lakes, maple syrup and Justin Bieber. The editor-at-large for Toronto’s National Post argues that a complete merger of Canada and the United States would create a global colossus, add 13 stars to the American flag, eliminate the border and require just a few amendments to the Constitution. But, Ms. Francis acknowledged on a visit to Washington last week, not everyone up north is thrilled with the idea. “I wanted to attack the Canadian establishment and say, ‘Wake up, there is...