What is the test for changing a settlement agreement over custody?

There are two possible models for reconciling these competing values in the case of settlement agreements over custody. One is the “material change of circumstances test” set out in s. 17, and explained in Gordon v. Goertz. Once the threshold of a material change is reached, the whole issue is opened up. Finality, certainty and autonomy yield to changing circumstances. The other model is the two-stage test in Miglin. First the circumstances in which the agreement was made are examined, along with the broad policy values underlying family law. Then the agreement is measured against the present circumstances, to see if it still reflects the intent of the parties, and if it is still consistent with basic family law values. Under this test a premium is placed on autonomy and the need to protect settlement agreements as a way of achieving finality. Changing circumstances play a similar but lesser role under the second part of the test. Which test applies to an application to vary an agreement, not incorporated in a court order, over custody of and access to children? The choice between the Miglin test and the Gordon v. Goertz test (or possibly an entirely different test) is the key issue in this case.