as far as i know: i have to provide T4 with the other documents... right?
If it is on the document checklist, you have to provide it. Yes.
so the officer will compare it with the acceptable salary rate.
There would be no official reason for the IO to do this. However, if you're claiming to be an accounting supervisor but being paid like an accounting clerk, it may be a red flag that you aren't telling the truth.
Do you know any website provide this information?
What information? Wage information? The easiest way to get some idea is to go to www.jobbank.gc.ca and search the NOC code...