If it is such a good project and so necessary for the country, why did Harper push it through with a biased NEB panel,  with absurdly narrow terms of reference, no cross examination of the proponent's expert witnesses, and limited participation. Check out Robyn Allan on the process.
How can it be such a good deal when the markets we are hoping to reach already pay less per barrel - $8 less per barrel - than US refineries. Check out Jeff Rubin on pricing.
The process was flawed. The economics make no sense. 
Is there any guarantee that when the whole deal falls apart from lack of markets and low prices, the taxpayer won't end up paying for this blunder?
If Trudeau wants social licence for this project, he has to redo the NEB hearings with the new people already appointed. He has to included economics - markets, pricing - in the analysis. He has to allow cross examination of expert witnesses.
After that, if he still wants to do it, then he can.