The Caisse de Depot is cementing its plans to build a light-rail network throughout the Montreal area by saying it will connect to the metro system at three locations.

The original map for the REM showed stops in the same location as the Edouard Montpetit and McGill metro stations -- but the cost of those stations was never factored into the original $5.5 billion plan.

The Caisse's infrastructure division, CDPQ Infra, now says the stations with their connections to the Green and Blue Lines, as well as a station in the Peel Basin, will cost an additional $400 million.

The Peel Basin station would actually be underwater.

"We're sending a strong message that we will have a strong downtown with the fluid transport," said Montreal Mayor Denis Coderre.

Macky Tall, the Executive Director for CDPQ Infra said there were several difficult technical challenges that needed to be overcome in order to connect a new train line to the metro system.

"At l'Université de Montreal you're under Mount Royal. That's 70 metres deep, that's like 20 storeys high," said Tall.

In order to bring people to the surface, the station will have banks of high-speed elevators designed to make the trip in 20 seconds.

Those elevators will ferry 5,000 passengers per hour.

The McGill station had other problems, including squeezing two exits into limited space.

One other station that appeared in Montreal on the original map has been eliminated in favour of the Peel Basin station, while another station proposed for the South Shore has not yet been finalized.

Caisse de Depot president and CEO Michael Sabia proposed the REM network in April, and since then has heard from area mayors with their wishlists for facilities that should be included at the stations.

At the same time many groups used the BAPE hearings to criticize the project, saying it not only encourages urban sprawl, it also cuts down on how many people will be able to use public transit -- especially for those currently using the Mascouche train line.

In order to operate, the REM would have to take over the Montreal-Deux Montagnes train line, and take over the existing tunnel that runs through Mount Royal.

CDPQ Infra told an environmental hearing in August that Via Rail, which is proposing a high-speed intercity train between in the Windsor-Quebec City corridor, would not be allowed to use the Mount Royal tunnel.

On the positive side, Sabia said the connection at McGill means a trip from downtown to Trudeau airport would take 18 to 20 minutes, instead of the 25 minutes initially projected for a trip from Central Station.

The report from Quebec's environmental group is expected to be delivered by the end of the year.

CDPQ Infra said Friday it is willing to put up $3.1 billion, while Montreal is willing to contribute $100 million for the Montreal stations. The federal and provincial governments are being asked to pony up $2.7 billion.

The electric train network is exactly the kind of project the Canadian government should want to support said Sabia.

The Liberal government has put forth a ten-year plan to invest in infrastructure and also aims to reduce greenhouse gas emissions.

Sabia said he expects Quebec and Ottawa to firm up their commitments within four months.

"I think there's a very high level of interest in Ottawa. We've got work to do, they've got decisions to make, that's their job," he said. "I feel very good about what we're accomplishing here, very good about the quality of the discussions with the government of Quebec, the government of Canada. I feel very good about where we are. I think we're in the process of accomplishing something very important here."

Construction is set to begin in the spring and be completed by the end of 2020.

The light rail system is expected carry 30.6 million passengers in 2021 and reach 42.7 million a year by 2031.