Follow the PGP2019 instructions, you will see that Sponsors who live in Quebec are not suppose to send their proof of income.
The federal agency will receive your application, after that they evaluate that you are eligible to sponsor your parents, they will give you a letter saying that you can move to the second step.
On the second step you will send the Kit B to the Quebec govt that will check your financial eligibility (which is "easier" than the federal and it's the Quebec govt who defines ). After that you pass this step, you will receive a CSQ from Quebec (actually your parents ) and them they will be able to apply to the permanent residency under federal laws on a third step.
So, on one hand you only need to prove 1 year of income (instead of 3 ) on the other hand your process has 3 steps instead of everything been done on a single one.
Basically this is the difference