“The court can consider the necessity to vary the custody and access arrangements if the parents’ relationship has deteriorated to the point where they can no longer cooperate. Tu v. Tu (2000) 2000 CanLII 22591 (ON SC), 7 R.F.L. (5th) 178. However, just because the parents have some disagreements over childcare decisions, the court should not for those reasons alone vary a joint custody order. Cabral v. Cabral [2000] O.J. No. 1092.
In particular, the decision of St. Pierre v. St. Pierre 2005 CanLII 14007 (ON SC), [2005] O.J. No. 1669 confirms that where joint custody of the child had worked for three years, the breakdown in communication between the parties was not a ground for varying the joint custody order to provide sole custody to the mother. In that case the children enjoyed an exceptionally close relationship with the father.
The court must consider all relevant factors and the relationship of the parents to ensure there is no power imbalance or other factors which would make joint custody unworkable.
An ongoing dispute between parents and their chronic difficulties in resolving parenting issues causing emotional and physical stress on the child can be grounds for varying the joint custody order made to provide for sole custody to one parent. Sterling v. Sterling [2005] O.J .No. 1936. Griffin v. Bootsma [2004] O.J. No. 2781 varied 2005 CanLII 35095 (ON CA),[2005] O.J. No 4112 (Ont. C.A.).”: