I'm trying to cut through the political propaganda and determine what the eventual destination would have been for the oil that would have flowed through the now canceled extension of the Keystone pipeline.
Before we get into that discussion, it's helpful to have an overview of the grades of crude oil. The lighter the crude oil (i.e., the less viscous it is and the lower the bituminous content) the more efficient (and less costly) it is to distill and refine it into end products like gasoline, aviation fuel, heating-oil, etc. Also important is the amount of sulfur in the oil (with less sulfur being more desirable). Crude oils that have low concentrations of sulfur are said to be "sweet", while crudes with heavier concentrations are said to be "sour". Oil that is light is very often sweet as well, hence the desirability of "light, sweet crude oil"
By way of examples, some common crude oils, in order from lightest to heaviest:
Brent Crude - From the North Sea
West Texas Intermediate (WTI)
Bakken Crude - This is the crude extracted from the Bakken Shale in the Dakotas and Western Montana
Athabasca Bitumen Blend (ABB) - This is what's extracted from the Alberta tar-sands.
Note that Canadian ABB tends to be quite a bit heavier with a MUCH higher sulfur content than the oil extracted from the Bakken Shale. Because it is more difficult to refine, it sells at a considerable discount compared to the other crude oils listed above.
In 2008, when companies in Canada first proposed building a pipeline to connect the Athabasca oil fields to refineries in the American Midwest and Gulf Coast, it seemed like an economically feasible plan. In fact, it was so economically feasible, that the majority of the Keystone Pipeline network got built and is currently operational. In the intervening decade though, the shale oil industry (especially in the Bakken Shale) in America exploded in terms of shipped volume, and the bulk of the refiners retooled to be able to process Bakken Crude, which is quite a bit lighter and sweeter than the crude oil coming out of Canada. With American refiners effectively unable to process increasing volumes of heavy, sour crude, that means the Canadian crude has to be sold to countries with the ability to refine this viscous, dirty, sludgy oil into useful products.... and that means, mostly, China.
An interesting note: if one were to claim that it's important to keep that Canadian crude in the United States, it would mean exporting increasing quantities of oil extracted from the U.S. to foreign markets and retooling American refineries to process this dirty, difficult crude oil being imported from Alberta. (The U.S. export ban on crude oil was lifted in 2015)
In the end, the oil from Alberta's Athabasca tar-fields will almost certainly still make it to China. The Canadian government purchased the Trans-Mountain Pipeline from Kinder Morgan in 2018 and is currently expanding its capacity in order to carry the crude oil from Alberta westward to British Columbia, then to be shipped on tankers to Asia.
I don't have a strong opinion one way or another on canceling the final extension of the Keystone pipeline, and I suspect that in terms of pollution and land-use, it's a wash. The only way to seriously address the environmental and land-rights issues associated with the Athabasca oil sands is up to the government and people of Canada, and is entirely out of American hands, regardless of whether or not the XL extension of the Keystone pipeline gets built.