What is the threshold for variation of a custody order?

Gordon v. Goertz discusses the threshold for variation of an existing custody order that permits consideration of a claimant’s application to vary a custody order to allow her to move. At paragraph 13, Madam Justice McLachlin, who was then a Justice of the court, writes that before entering on the merits of an application to vary a custody order, the judge must be satisfied of a change in the condition, means, needs or circumstances of the child and/or the ability of the parents to meet the needs of the child that materially affects the child and that was either not foreseen or could not have been reasonably contemplated by the judge who made the initial order.