It depends, does anyone know if the same form is used to pay the fees inland and out land?
If that's the case (that they are the same), I would pay the fees and then submit the proof that you are going to be applying for PR with your visitor extension application to show proof you are not just trying to live in Canada on a visitor visa and give more merit to your visitor visa extension application. I am almost certain you must maintain legal status in Canada when applying out land so this is very important.
If I were you, I would find out if I could get the extension asap, because in your case, it basically chooses for you what route you should go (inland vs. outland)
Do you have a single entry visa or multiple?
To add, when you do your medicals make sure you tell the doctor it is for OUTLAND process if you decide to go that route. I have been told the medical documents for inland/outland are different, and with immigration, you can never be too sure.