Real world highway mileage in cars I've driven and measured, in miles per US gallon (not imperial gallons)
2006 Honda Civic 1.8L = 41mpg with air conditioner running
2010 Toyota Corolla 1.8L = 40mpg with air conditioner running
2005 Nisssan Altima 3.5L V6 = 32mpg with air conditioner running
Those are pretty close to the Canadian highway ratings.
I keep track of mileage every time I drive between Edmonton and Cold Lake, about 180 miles one way, and the first two cars consistently nailed those numbers. The Altima belongs my parents and their trips are usually between Edmonton and Chilliwack, about 630 miles each direction.
As long as you're not driving like a retard, you'll get very close to the Canadian ratings. If you drive like a retard
or drive in very dense traffic, you'll get the US ratings.