The question: Would oil from the Keystone XL pipeline compete with Bakken oil if the new pipeline is built?
The answer: Canada crude is heavy, so it needs to go to refineries set up to handle that particular kind of crude. There are some of those in Alberta, but many are on the Gulf Coast.
Refineries cannot readily switch from one type of crude to another, so if the refineries set up for heavy crude cannot source it from Canada, they will have to get it elsewhere. That means places in South America like Venezuela, as well as places in the Middle East, such as Saudi Arabia and Kuwait.
Bakken oil, meanwhile, is light sweet crude. It requires different processes to efficiently refine. While some refineries do blend in some light sweet crude for their process, in general this doesn’t change the amount of heavy crude a given refinery will need.
This means the two types of oil are not really in direct competition with one another.
Keystone XL might have helped Bakken crude, however, because the project was to include an on-ramp for up to 100,000 barrels per day of Bakken crude oil. This would have eased pipeline congestion during the boom, if the pipeline had been allowed to move forward.
It could also still help ease future congestion in the Bakken. Production from the region has been projected to continue rising once the current pandemic, price-war induced supply glut has balanced.