It's been a while since I did my written exams but at the time there was 1 written exam for the CPL, 2 ATPL written exams (HAMRA and HARON), and 1 INRAT written exam (IR). I've got no idea what you'd have to do with regards to conversion/flight testing and whether you can just do one flight test for the ATPL (H) - bear in mind that in Canada you do need to hold a Canadian Night Rating to hold an unrestricted ATPL(H).
Transport Canada can be contacted/emailed fairly easily. Just search their website www.tc.gc.ca for whichever regional office you want to speak with and they should answer your questions.