North Dakota has saturated rail and road traffic trying to get it's crude out of the state. At the same time Natural gas is simply being burned off because there's no pipeline infrastructure to transport it. Pipelines that were being used to transport natural gas to the midwest from the east coast and gulf states will no longer be able to be used next year because they are being converted for use in transporting chemicals needed for tar sand conversion in Canada.
The reason big oil companies want the pipeline from Canada and not North Dakota is because there's a multibillion dollar tax loophole related to foreign oil processed in US refineries for export. Which is why the pipeline runs to the coast. Keystone Excel will have no effect on US fuel prices because it's not designed to sell fuel on the US market. It's quite likely that Keystone will result in refining capacity being taken out of the US market as it's used for export. All the signs point to this project actually costing the tax payer more at the pump in the end.
Let's also not forget the natural gas problems this creates for the upper midwest. They currently get their natural gas from Canada. Tar sand production need incredible amounts of natural gas. That's expected to increase prices people will be paying to heat their home. At the same time there's no plans now or in the future to bring more natural gas to upper midwest from the east coast. If anything they are losing capacity in order to support the tar sand production.