The Northern Gateway pipeline has to cross Crown lands in BC to reach the coast. To cross these lands the company has to apply to BC for an interest in the land. Nowhere in BC legislation is there anything that says that the BC government has to grant any form of interest to Enbridge for their pipeline.
Enbridge has to come to BC and ask to use the land and BC is allowed to say no.
Lands are under the control of the provincial Crown, not the federal Crown in Canada. In the case of BC Crown lands were under the control of BC before it joined in Canada in 1871. As opposed to the prairies or northern Ontario and Quebec, BC Crown lands have never had any underlying federal Crown allodial title . The route of the pipeline in BC is owned by the government of BC, not Enbridge, not Canada and not Alberta. In BC the First Nations have a much better claim to lands than the federal Crown does.
The federal government could in theory try to expropriate but the federal government is not building the pipeline so they have has no direct interest or reason to expropriate the lands. Also, expropriating land to benefit one private company would would violate NAFTA and the new Canada China free trade agreements among other agreements. The core of most free trade agreements is that governments to do not favour one company over another one, expropriation is a tool that violates this in the most fundamental way when done on behalf of a private company.
The best reason I know of that the federal government has had to expropriate lands would to settle Treaties with First Nations - guess what, this is apparently not a good enough reason to be able to succeed. If it had been the federal government could have settled the Nisga'a Treaty in 1977 and not 1996.
Expropriation for a single proposal from a private company sets a horrific precedence. In the case of the Northern Gateway pipeline there are numerous other options for the the oil industry that they can pursue if this pipeline is not built. They could build a line to Churchill Manitoba. or to Thunder Bay, or use rail cars, or ship more into the US, or refine it in Alberta, or build a pipeline through to Cherry Point in Washington. There are no shortage of other options. There is no critical and fundamental reason why the Northern Gateway pipeline needs to be built.
The federal government could make BC's lands laws null and and void through the federal power of disallowance, I think. I am not sure they can do this for laws already in place and it has to be done by the Lieutenant Governor of BC. Even though this is a right the federal Crown has, I am not sure that legally they could use it in this case because it certainly does not seem to be what was envisaged the power would be used for. The power seems to have been created as a way for the federal Crown to disallow a recently passed provincial law that is clearly unfair, illegal or interferes in federal Crown powers. None of this applies in this case. Also, since this power has not been used in about 70 years and the emerging nature of Canada is that this is a lost power of the federal Crown.
If the federal government were to try and use the power of disallowance or any sort of massive expropriation would ensure all the provinces would be in direct and total conflict with the feds. It would destroy the popularity of the Conservatives and lead to the demand for a re-writing of the constitution to reduce the powers of the federal Crown. It would also put BC and Canada in the courts for years to resolve the legal issue. While is was before the courts there would be no movement on the pipeline.
A very interesting upshot of the federal government using expropriation would be First Nations' ownership of the land. There is a good case for the First Nations to have a higher and more pressing right to any lands the federal Crown acquires. It also means in BC the federal government becomes more or less obliged to use expropriation to settle Treaties in BC.
What all this means is that BC has a veto over the pipeline. If BC says no there is nothing anyone will be able to do about it. If Enbridge, Alberta and the federal government want to see this pipeline, they should be bending over backwards to address the issues of BC and of First Nations.