Quebec's public pension fund said on Thursday construction of the world's third-largest light rail system in Montreal will cost $6.3 billion, $400 million more than expected, and will take longer to complete.

The Caisse also said a consortium led by SNC Lavalin had won a contract to provide engineering, procurement and construction on the project. A consortium led by Alstom and including SNC Lavalin will provide rolling stock and systems.

Bombardier, the plane and train manufacturer based in Quebec in which the Caisse is a major shareholder, was not selected in the process which was overseen by an independent committee.

The Caisse is both financing and overseeing the construction of the 67 kilometer (41.6 miles) public transit system in Montreal, the third-largest automated transportation system in the world behind those in Dubai and Vancouver.

The fund said that construction will begin in April with initial testing of the track to be conducted at the end of 2020 and the first riders boarding trains in the summer of 2021.

The Caisse had previously said the project would cost $5.9 billion in total, of which it would provide $3.1 billion. The rest of the funds are being provided by Quebec's provincial government and Canada's federal government.

The Caisse will own and operate the track once it has been built. It had originally stated that the first trains would be running by 2020.