Thinking of driving from the U.S. to Canada (or vice versa)? Whether the reason is for business or pleasure, it's much easier to find a rental that allows U.S. / Canada border crossings than a rental that allows U.S./Canada to Mexico border crossings. Like any other rental car policy, there are stumbling points -- it's much more difficult to find a rental that can be returned in the other country than finding a rental that can be driven across the border and then returned in the original country.
Why did I want to drive a rental car to Canada? The short answer was to escape Tennessean summers and use my free 150th Anniversary Parks Canada pass while singing the Canadian Railroad Trilogy. Rather than putting thousands of miles on my personal car, I instead opted to put thousands of miles on Hertz's car (Canada, like the U.S., is a very big country).