The short answer: Gas is more expensive in Canada.
At this moment, the US dollar and the Canadian dollar are at par, but there may be wild swings in a relatively short time. Ex: In November the Canadian dollar was 10% higher than the US dollar. Economists predict (what that may be worth I don't know) that the tendency might be a Canadian dollar above par, as your current President does not seem very gifted to manage the economy.
At present regular gas is from 0.93$ to 1.19$ a litre. Gas is sold in litres in Canada, 3.79 litres make one US gallon, so a US gallon is from 3.52$ to 4.51$.
Generally speaking, diesel is a little cheaper than regular gas most of the year in most areas, but may be a little more tha regular gas in winter
To check out current gas prices in the US and Canada, here is a link:http://www.gasbuddy.com/
Hope this helps.