Moving on ...
As
@foresterab notes, it is is easier to work within boundaries than it is to cross boundaries. Each province can build up to its boundaries but needs approval from the neighbour and/or Ottawa to cross the boundary. A good chunk of the Keystone XL pipeline to the US boundary has already been laid.
I am sure there are many potential cross-bondary points of approach between AB and BC and between AB and SK.
The issue then becomes how does one legally cross the boundary.
In World War 2 Canadians resorted to convoluted measures to procure American planes with American connivance. Due to neutrality laws the Yanks couldn't ship aircraft to Canada. So they parked them at the border on the American side and the Canadians lassoed them and dragged them across. Honour was satisfied.
The modern work-around is the railway. The US permits trans-boundary shipping of oil by rail even when it fails to approve pipelines. In Canada the provinces can't prevent the transport by rail, across their boundaries, of approved cargoes and oil is an approved cargo.
Pipelines are more efficient but needs must.
One work-around is to ship oil by rail to Prince Rupert, Churchill and Saint John, New Brunswick.
Pipelines are cheaper and safer as the people at Megantic can vouch.
Individual provinces could opt to make the transportation safer by permitting pipelines within their own borders to save their taxpayers from managing the rail risk.
Failing that degree of co-operation there doesn't seem to be anything to prevent a pipeline terminating outside but adjacent to the boundary of the unco-operative jurisdiction and transferring the oil to rail cars (or for that matter Seaway tankers) and shipping by rail to the next pipeline terminal.
New Brunswick could build a receiving terminal to serve its own pipeline to serve the maritimes. It would probably be cheaper to deliver oil by pipe to Nanticoke or Sarnia but then you have to factor in seasonality, just as would happen at Churchill.
...
If the pipe and rail combination is chosen then the safest and most efficieny system shortens the rail exposure and lengthens the pipe. But if the only way over the border is by rail then the shortest rail transfer is a tanker parked on a siding that straddles the border with one end in either jurisdiction. Jurisdiction A delivers its oil to the railway which then delivers the oil to jurisdiction B and the rail car never moves. Jurisdiction A fills it. Concurrently jurisdiction B empties it concurrently. The tanker becomes a wide spot in the pipeline.
I am sure this has already occured to others and the lawyers have already got it covered .... but I like to speculate.
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