Sure the Joint Review Panel gave their conditions under which the Northern Gateway pipeline could be built, but they have no jurisdiction over the land.
To build the pipeline Enbridge will need a legal right of way. Most of that right of way will cross over provincial Crown Land. Enbridge will have to apply to the province for the tenure to the land and the province can say no.
The federal government can not issue tenures on provincial Crown Lands, that is Ultra Viries. The province is the only Crown with the power to create new legal tenures for BC provincial Crown Lands. The federal government would have to expropriate the land from the province and make it federal Crown Land. Doing this would cause a legal nightmare for a host of reasons.
1) Jurisprudence in Canada on expropriation has changed and taking land from a province for the benefit of a private corporation that is unwilling to meet provincial standards is not likely to constitutional. If this were for the needs of the Armed Forces, the feds might be able to expropriate, but do so because a company is not willing to come to agreement with the province is not realistic.
I can see the courts saying No to the feds because BC has had a clear position on the conditions it has for the pipeline and Enbridge did not try hard enough to meet them.
2) The federal government has long taken the position that it can not expropriate provincial Crown Lands to meet the needs of Treaty settlements. The fact they have expressed their belief they could not expropriate for aboriginal people and were to then do so for a private for profit company means they are opening themselves up to very serious and expensive lawsuits from all the First Nations in BC for compensation.
The federal government has a constitutional obligation to deal with First Nations in an honourable way and they have a fiduciary duty to ensure they do the best by the First Nations. If they could have settled Treaties without the province through expropriation but did not do so they are now liable to four decades of screwing around not settling Treaties. Based on Apassasin as a value precedence, conservatively the First Nations could legitimately win a law suit worth $50,000,000,000 and ownership of 100,000 square kilometers of land in BC. That very serious threat alone is enough reason for the feds not to want to go down the path of expropriation.
Without expropriation BC has a veto over the project.