You have to decide in what program you want to study in,
You then will have to apply (in can be a long process to gather the different letters of references + filing the application + letter of motivation + official transcripts and courses descriptions).
For most of Universities, the dead line for September is in march
+ be prepared to pay crazy tuition fees as an international student.
I work for the University of Ottawa, so don't hesitate to contact me for more info.