Natural gas pipeline will extend 530 kilometres and carry up to 670 million cubic feet of natural gas per day.
Pipeline-giant would convert its natural gas mainline to ship crude oil to refineries in eastern Canada and the US.
Grand Rapids pipeline will stretch 500km, carrying oil sands crude and diluent by 2017.
Pipeline was shut down last week over safety concerns.
Pipeline company is investigating a small “anomaly” on the outside of the pipeline, which will be shut down for three days.
Canadian pipeline firm awaits approval for two other sections of the 780 kilometre pipeline.