In short you could not export Canadian oil to foreign markets, without first refining it. This would mean that greater refining capacity would have to be created, with consequent permanent employment.
The market for more refined product shipped from the Eastern seaboard is zero [or less].
Irving and the Ultramar plant in Quebec are interested in conventional oil that could be brought on the East West pipeline. But they are not interested in upgrades that would be required for refining bitumen. The margins in Eastern refining are very thin.
Being able to ship Western "sweet" crude is just a financial bonus for TransCanada- the driver, without which the project stays on the drawing boards, is being able to ship bitumen
Irving is keen to build the export terminal.