It is kind of impossible to say whether the 407 ETR received "fair market value" because there was no market existing prior to the lease.

What is clear though is that there were multiple bids put in on the 407 ETR lease in an open and transparent bidding process and the government selected the highest bidder suggesting that they received pretty good value at the time.

A few years later parts of the 407 ETR were traded at a price that gave a much higher valuation for the lease, but that was after the highway, was operational and the revenue stream was well established, was extended to nearly twice the length and had generally reduced the risk on returns.

Hindsight being 20/20 the government might have done better waiting a handful of years to lease the 407 ETR and shouldered the risk.  On the flip side that could have blown up in their face if they mismanaged the highway.