I'll probably be better prepared to answer that question in a year. Kevin and I are currently working on exactly that project. The Quebec reforms offer a couple of really good opportunities. One, as has already been mentioned, is this period of time reserved for fathers. One huge gap in research is the possible effects of paternal care during early childhood. We don't have a lot of evidence. Intuitively, it seems good that fathers are at home, but we don't have a lot of studies that look into that.
The other big gap in the literature--again, some of this might seem odd, and we don't have a lot of evidence on it--is how people's choices respond to income replacement rates. The Quebec reforms offer shorter leaves, with higher replacement rates. We're hoping to use those changes to see how people respond to them to get some idea of how much more likely it is that people stay home. Do they stay home longer if their incomes are replaced at higher rates?
Kevin may be writing those data today.