TORONTO -- Ontario is partnering with a global real-estate company to build a new GO Bus terminal in downtown Toronto, which will become part of an integrated transport hub at the Union Station.

The province said Tuesday its regional transport agency Metrolinx will join Montreal-based Ivanhoe Cambridge to build the project, starting next spring.

Once construction of the terminal is complete in three years, it will bring intercity bus services, GO Transit, Via Rail, Toronto transit service and the new Pearson airport express train to the hub.

As part of the deal, Metrolinx has agreed to sell the current bus terminal on the north side of the tracks to Ivanhoe in exchange for a 99-year lease of the new bus terminal located at the base of a proposed office complex on the south side.

The complex will have two towers with up to 250,000 square metres of office space and a landscaped, elevated sky park over the rail corridor. It will eventually connect to the PATH system.

Ivanhoe will invest about $2 billion in the project, while Metrolinx will spend about $100 million. But both companies stressed that the figures are just initial estimates.

"Today's announcement of a new GO Bus terminal at Union Station with commercial space above it aligns perfectly with our government's plan to create transit hubs integrated with sustainable employment developments," said Transportation Minister Steven Del Duca.

He added that the new terminal will provide more options for travellers in the Greater Toronto and Hamilton Area.

The Union Station is already the largest inter-regional and multi-modal transportation hub in Canada and serves twice as many passengers as Pearson airport, Del Duca added.

"We want this project to be iconic for Toronto through inspired design and intelligent integration of public transit with green spaces," said Ivanhoe CEO Daniel Fournier.

In promoting the project, he also cited a global shift of people toward downtown areas.

"More and more people, young and old want to be closer to the centre of the action. That affects urban transportation and it affects our long-term view of the office market."

According to the province, GO Transit carries about 66 million passengers per year.

On a typical weekday, it is estimated that GO runs almost 250 train trips and more than 2,500 bus trips that carry about 250,000 passengers.

A subsidiary of the Quebec pension fund Caisse de depot et placement du Quebec, Ivanhoe has more than $40 billion in assets mainly in Canada, the United States, Europe, Brazil and Asia.