Hi
( You have to study 2 years in same or rellevant course to get an 3 yeras PGWP ).
This is what , you will get if you call CIC about this .
But , in actual it depends .
I have seen a case , in which a student took 2 years to complete a 8 month course and got 3 years PGWP.
and one more case in which , a student got 3 years PGWP with 1 year course in sheridan and one year in st. lawrence (I bothh irrelevant courses )
So , it actually depends how you apply and the visa officer .
You can say , it depends on luck though.
As it is a one time chance , apply with all of your 4 sem transcripts and explain why you took another course , how it can help you in future .
NOTE :- please don't mention you took it for 3 years PGWP.
As far as i know , If you will do it right . You can get a 3 years PGWP easily .