That's a good question. It doesn't make any sense to stop accepting Canadian credit cards, when you are trying to make inroads in Canada, and with the dollar the way it is, more Canadians are travelling into the USA. We are getting close, so I checked a couple sites and was shocked to see it. I75 online says it is for pay at the pump, the other two say they don't recognise it at all. Either way, it will be another option on our trip.
One opinion that was raised, was that Pilot's former president (by title only, he still runs it through his family) Bill Haslam, is a big proponent of gun registry (Mayors for gun control), and it is costing him votes and business, so he is trying to use some anti-Canadian stance to garner some redneck votes. Still makes little sense to me.