Well it used to be at least. Metric was a unit in 1799. Canada got metric in 1970.  
  
Edit: 
It is still used in Canada (on the railways). 
Found on Wiki: 
These include roads in the United Kingdom, the United States, and UK and US territories; American Samoa, the Bahamas, Belize, British Virgin Islands, the Cayman Islands, Dominica, the Falkland Islands, Grenada, Guam, Burma, The N. Mariana Islands, Samoa, St. Lucia, St. Vincent & The Grenadines, St. Helena, St. Kitts & Nevis, Turks & Caicos Islands, the U.S. Virgin Islands, Antigua & Barbuda (although km are used for distance), and Puerto Rico (same as former).
Miles per hour are also used in the Canadian rail system. In some countries it may be used to express the speed of delivery of a ball in sporting events such as cricket, tennis and baseball.