Apply any time you want but if you get married before you land as a PR, you must let them know. Even if they have already issued you the PR visa when you get married, you must send your passport back to them to let them know and they would then cancel your visa and issue a new one later to you and your wife. If you have no problems proving that you did not live together before marriage, then there is also no problem if you land as a PR before you marry to sponsor her later. You would have to be in Canada to sponsor her though and she might not get a TRV to join you so you would be apart.
Your plan of applying in October and then informing them when you get married in December should work out fine. Then you and your wife will get your PR visas at the same time and can go together to Canada.
Your plan of applying in October and then informing them when you get married in December should work out fine. Then you and your wife will get your PR visas at the same time and can go together to Canada.