You can sight case law on the matter to the following:
Date: 2011-09-09
Docket: DF 2217/09
URL:
CanLII - 2011 ONSC 4305 (CanLII)
Citation: V.K. v. T. S., 2011 ONSC 4305 (CanLII), <http://canlii.ca/t/fn2r2>
Here are the specific paragraphs to thwart an ill advised parent against trying to claim joint custody won't work... The alternative is Parallel Parenting.
[71] The Ontario Court of Appeal’s approach to joint custody has evolved over the years. In Kruger v. Kruger[18] and Baker v. Baker[19], the court held that joint custody is an exceptional remedy that should only be granted in circumstances where the parties demonstrate co-operation and appropriate communication, and are willing to try a joint custodial arrangement.
Since that time, the court has dropped the requirement of consent to a joint custody order, but has maintained that in order to grant joint custody, there must be some evidence before the court that, despite their differences, the parties are able to communicate effectively with each other.[20] The rationale for this principle is that the best interests of the child will not be advanced if the parties are unable to make important decisions regarding the child under a joint custody regime.
[72]
While some measure of communication and cooperation between the parties is necessary to support a joint custody order, the court is not required to apply a standard of perfection in assessing the ability of the parents to work together. As Quinn, J. remarked in Brook v. Brook, “the cooperation needed is workable, not blissful; adequate, not perfect.”[21]
[73]
A mere statement by one party that there is an inability to communicate will not be sufficient to preclude a joint custody order. The court must carefully consider the parties’ past and current parenting relationship to obtain the “big picture” respecting the parties’ ability to communicate,
rather than simply relying on allegations of conflict by one or both of the parties, or a snapshot of the situation that exists at the time of trial.[22]
[74] The existence of conflict and strife between the parties from time to time
will not necessarily preclude the court from making an Order for joint custody. The question to be determined is whether the conflict between the parties is impacting or likely to impact on the well-being of the children. If the evidence indicates that the parties, despite their conflict with each other, have been able to communicate, shelter the children from the conflict reasonably well, and put the children’s interests ahead of their own when necessary, an order for joint custody may be appropriate.[23]
The question for the court to determine is “whether a reasonable measure of communication and cooperation is in place, and is achievable in the future, so that the best interests of the child can be ensured on an ongoing basis.”[24]
[75] Where an objective review of the historical and more recent evidence clearly indicates that there has never been an ability to cooperate or communicate effectively, or that one or both of the parties is/are unable to put the needs of child before their own, joint custody is not an appropriate order.
[25] In these circumstances, hoping that communication between the parties will improve once the litigation is over does not provide a sufficient basis for making of order of joint custody.[26]
[76] In analyzing the ability of the parties to communicate,
the court must delve below the surface and consider the source of the conflict. The Ontario Court of Appeal has clearly stated that one parent cannot create conflict and problems with the other parent by unreasonable conduct, impeding access, marginalizing the other parent, or by any other means and then claim sole custody on the basis of lack of cooperation and communication.[27]
It is a useless argument even solicitors try to make even today considering the stacks of case law in contravention of the "belief" that one party can claim sole custody and EOW based on "communications challenges".
Good Luck!
Tayken
and good move getting the doc on board. 
