It would be interesting to know the comparison of east-west traffic that is actually by-passing the GTA versus that which is travelling within it, because if the latter is known to be significantly greater, then a northern east-west connector won't likely be financially viable without inducing sprawl. Ditto for Hwy 400 traffic; comparing trips that continue east or west to points beyond against those that terminate locally.
Agree with the perspective that, if the government wants to break a contract, try the 407. If they are firm to their beliefs, go big or go home. On the other hand, I believe the Beer Store legislation will end in a negotiated settlement, which they will claim as a win for the people. The amount at stake in Hwy 407 would likely make a negotiated settlement too rich.