First of all, thank you for the reply, I too believed it is possible to get 3 year permit, but I can't help to notice the note that was written below it
If the officer notes that the duration of studies was shorter than the duration of the program, as indicated in the letter confirming the completion of the program of study, and the program was not completed in an accelerated form, the post‑graduation work permit may be issued in accordance with the duration of studies. For example, if the applicant undertook classes for a period of 12 months, not in an accelerated form, but their degree notes that it is a 2‑year degree, the post-graduation work permit may be issued for 12 months, in accordance with the duration of their studies.
The above paragraph which was written in the cic website is really confusing, it's kinda states that 2 year course with 16 month actual study will given only 16 month permit, which means almost all the people who apply to diploma will get 16 month permit only, I would be very happy if you could enlighten me about this