The last on-record year in Canada where sole-custody (maternal) outpaced joint custody was 2002, where the numbers were 49% - 42% with the remainder being sole-custody (paternal). The reason that the joint custody cases are now "in the lead" so to speak is because the courts have rejected some of the older case law. One example is the tender-years doctrine which basically encouraged sole-custody to mothers for all children under the age of 6. The belief was that mothers were psychologically better equipped to deal with the needs of small children. Nowadays, we no longer hold these views, but I would caution that while it sounds harsh, it isn't necessarily a malevolent idea. Remember that for a long time, mothers stayed home with children before they went to school, so that the bond between mother and child was different (not better necessarily, but different) than that of the father and so many child psychologists would testify to this. In any event, this doctrine is outdated and has been struck down by the courts, except in the obvious examples, like babies and toddlers who are still being breastfed in which case the mother almost always gets sole custody on a temporary basis to be revisited based on a specific timeline.
There are other burning issues now - for example, you have more women reporting incidents of domestic violence than ever before. The question is, if the father did not physically abuse the children, but the children watched him abuse the mother, should that be a determinant in custody cases?