Mauricio's got it.
NRCan is showing miles per Imperial gallon, and we're still using ratings/test methodology that are roughly equivalent to the "old" (pre-2008) EPA values.
For 2008 onward, EPA significantly
revised (down) its ratings for all vehicles to make them more "real world", and we did not follow suit. Before that, ratings between the US & Canada used to be pretty similar.
EG: You can see the size of the resulting ratings differences (city MPG, all converted to US gallons) of four sample vehicles in this thread:
http://ecomodder.com/forum/showthrea...ion-23772.html . Compare the EPA city vs. NRCAN city values on the charts.