The sale to a joint venture owned by Axium Infrastructure Inc and Manulife Financial Corp is part of a plan to raise C$2 billion of the C$8.4 billion WGL deal.
AltaGas, which will remain the majority holder of the projects, said it expected the transaction to close by the end of June.
"We also continue to advance discussions for the monetization of certain additional assets, which we expect to conclude in the third quarter," Chief Executive Officer David Harris said.
The projects include the 195-megawatt Forrest Kerr Hydroelectric Facility, the 16-megawatt Volcano Creek Hydroelectric Facility and the 66-megawatt McLymont Creek Hydroelectric Facility.
TD Securities Inc, J.P. Morgan and RBC Capital Markets acted as joint financial advisers to AltaGas.
(Reporting by Karan Nagarkatti and Laharee Chatterjee in Bengaluru; Editing by Anil D'Silva)