The application process for (most) Canadian schools is a little different. When you apply to a program you aren't accepted as a general entry student like with most US schools. Instead, you are given an offer or offers to work with one or multiple Profs. The admissions committee will look through applications and decide on potential students that meet their criteria and then applications are sent around to potential supervisors to look at. The final decision on accepting a student is up to the Professor, who will be the source of the majority of a students funding. Generally, Professors will conduct interviews somewhere from January to March with students they are interested in and will give students an informal acceptance followed by an offer letter from the department after a week or so. Because of this, there isn't a set date that schools will release results, it's an ongoing process.
Rejections are very slow because the department needs to get a no from every Prof before they are sure and may just wait until every Prof has made a decision on every student before sending out rejection emails. Getting these in mid-late April or even May is not uncommon. Generally, it is a good idea to have contacted potential supervisors in advance to let them know you're interested in working with them and they can let you know if they have room in their group or not. If you haven't been contacted by a Prof by April for an interview or telling you that you're on their waitlist then you can usually expect a rejection that will come later.