Yes, even if they gave the line away for free they'd be better off than today.
- As part of the purchase agreement, CN would retain trackage rights to continue serving the customers on the line.
- The Province would pay for maintenance, charging only minimal track fees (far cheaper than maintenance).
- The Province would pay to upgrade the line to much higher standards, so CN's freights would be able to do their runs much more quickly, using less equipment and personel time. Even if their trains get put in a siding sometimes to let a GO train by, they'd still get to their destinations faster than today.
The purchase price is not based on the amount of money which would make it worthwhile for CN, it's based on the amount of money that CN can get out of the Province, knowing that the governmnent has promised the public to provide regular GO service to London.
To this last point, I'm wondering if it would be a good strategic tactic to temporarily cancel the London-Kitchener GO Train service and introduce an hourly(?) bus service from London to Kitchener (which would also replace the PC Connect bus service which currently follows that route), and also a once-daily commuter train via Brantford, taking over the schedule of the former VIA commuter run which VIA apparently doesn't want to reinstate. The government can say that the promise of London GO train service was kept thanks to the south mainline GO service, and it continues to connect London and Kitchener with a faster GO service anyway.
I suspect that CN does want to sell the line, so if they see that upgrading the Kitchener-London railway isn't the Province's only option, they may lower the selling price to entice them to take the line over.