A question regarding work Permit after finishing my studies

[hamid123456]

There's something that I would be glad if anyone help me.

Right now, I have an admission from a university for Fall 2018 that its duration is 24 months. I am in the process of visa, and if I get my Study Permit, it will be issued for 2 years I guess.
After finishing my studies, I will get three years work permit.

Now I am trying to get admission for another program, which its duration is 16 months. So that after I get my Visa and Study Permit, I could change the DLI and study in the new program.

I have some confusion regarding my work permit after my studies. If I change my DLI to 16-months program, for how long my temporary work permit after graduation will be issued?

I mean, because they will probably issue my study permit for 24 months (Because my first admission which I requested Visa through that is 24 months in duration)

After I finish my studies, how will they know that my program was 16 months?

 

[hamid123456]

And one thing else.

Both the programs that I mentioned above are in Universities inside Ottawa. Do you thing that studying in a 16-months program will be enough for me to get permanent residence after that, or is it much better if I study in the 24-months program?

The most important reason that I want to change my program from 24 months to 16 months is financial matters. i may be able to get some funding for my supervisor for the 16-months program, and even if not, then 16-months program will still be cheaper than 24-months program to finish.