The difference in MPG
The difference in MPG Canadian VS US is the use of Imperial Gallons VS US Gallons.
The U.S. liquid gallon and the U.S. dry gallon are different units defined by different means. The U.S. liquid gallon is defined as 231 cubic inches and equates to approximately 3.785 litres. One imperial gallon is equivalent to approximately 1.2 U.S. liquid gallons.
Hence your MPG would be 20% higher.