There are 3.785 liters in a US gallon. The current price in Toronto went down to C$1.16/L. Therefore, a US gallon costs C$4.40. If you use a credit card, you pay about 90 cents for a C$. So that's $3.95 US. In the US, the price is about $1 less. So if you want to buy gas, don't come to Canada for it.
And especially not Vancouver where we are at $1.30/L these days. Was $1.55 in June and over $1.43 just in Aug/Sept.