Peter Lantin says the dispute has gone beyond the project proposed by Calgary-based Enbridge (TSX:ENB).
He says it's become the focus of the battle for aboriginal rights in a province where the Crown has dragged its feet for generations on settling claims.
Lantin says the federal approval has unified aboriginal groups on all sides behind the lawsuit, which is expected to be announced in the coming weeks.
Enbridge officials have said legal challenges were anticipated and they continue work to engage aboriginal communities along the pipeline route.
But a CIBC market analysis calls the government approval "largely academic at this point," and shares in Enbridge dropped the morning after the federal announcement.