The issues of custody and access are settled by considering the best interests of children. There is a presumption that children’s best interests are served when the children have access to both of their parents after a separation. There is an onus placed on the party wishing to limit a child’s right to have open access to the other parent. The onus is to rebut the presumption of maximum contact of the child with both parents.
The recent H.H v. L.H. Superior Court decision deals with such issues in an eloquent manner: http://www.canlii.org/en/on/onsc/doc/2016/2016onsc707/2016onsc707.html