Bad approach I guess.
If you will continue your studies with 1-year long program then you what you will do after completing of your studies?
You won't be able to do any job because you will have only study permit and your studies will be completed that time so you won't be able to work part time even.
If you will apply for PGWP after completion of your 1-year study program, your remaining 2-year study permit will be waste and you will get just 1-2 year PGWP on the basis of 1-year study program.
This is what you actually want?
Your 3-year long study permit won't help you in any case if you will attend 1-year study program. Neither you can utilize it to work after studies nor it will help in getting 3-year PGWP caz your study program will be of 1-year long.
So what actually your are trying to do?
After completing of your 1-year study plan, you can either start another study program or can apply for PGWP.
I have discussed the PGWP case above and if you go for another 1-year or 2-year study program then you may get long PGWP after completing it i.e 3-year PGWP based on your two 1-year study programs.
If you select three years of course make sure you studied for three years or consult your university international advisor for help. Some courses may be transfer from three years to four or two years but it varies from course to course. Secondly, If you think you can only study one year of your three years of course then there is no way you get PGWP. As it is requirement of CIC that you must provide them your college letter which stats that you have completed the course and you are graduated from the school.
So whatever you choose, decide wisely!