What destination address you give for receiving cards is irrelevant. What counts the most is where you are currently residing or more importantly what grounds do you have to move out to Ontario.
Since you have a job in Montreal, it would be tough convincing CBSA or CIC.
One way could be to interview at several places in Ottawa, get a paper trail of that and use it for landing.
Generally speaking CIC is more understandable of this situation as opposed to CBSA. So landing by going to CIC office on first Tuesday of Month for PR landing is better than going to border.
Even if you do go to border, Cornwall is a better option. Quebec border will give you a much harder time.
And remember, this is not as simple as a standard PNP. Regular PNP is just tied to a province. But Quebec is a province with a different PR program altogether.
In fact I am surprised that you were able to convince Ontario PNP and CIC of your intent of moving outside of Quebec.
Some personal notes: This is first hand info, coming from some one in similar but better scenario. Was working and living in Quebec while applying for PR, but had a job offer from outside Quebec. Then moved individually to join new job out of Quebec while spouse and kids remained in Quebec to complete lease / school year. I had job in a different province (was working for 3 months), pay stubs, driver's license every thing. Still CBSA gave me a hard time. First they were concerned about me, then after knowing they showed concerns about family staying in Quebec indefinitely. It eventually worked out, because I had a lot more proof but took one full day. So don't take chances and
a) get more evidence of intention of moving out of Quebec
b) Either land at CIC Ottawa office or land at Cornwall border.
