Borealis and the Ontario Teachers' Pension Plan are considering a joint offer for Britain's first high-speed railway, High Speed 1 (HS1).
HS1 has a 30-year concession to run the 68-mile line linking London to the Channel Tunnel.
The UK Government is selling the line to recover its budget deficit.
Bids will be accepted until 17 August, according to railwayage.com.
Bids are also expected from a consortium including Groupe Eurotunnel, Goldman Sachs Infrastructure Partners and M&G's Infracapital.
Another consortium of Morgan Stanley Infrastructure, 3i Infrastructure and Abu Dhabi Investment Authority is also bidding for the project.