Sorry but I still don't get your issue. Typically, after you declare non-residency with CRA, then you become a non-resident and they won't bother you. But this is not always the case, there is a chance that CRA will still send you a letter and demand you to file a tax return. If you receive that letter, then just reply them you are still a non-resident. Therefore, I am still very confused on your issue. If your date of departure is Jan 1, 2016, then you should file a tax return for year 2016 to state that your left Canada on Jan 1, 2016. Jan 1, 2016 will then become the date you become non-resident. So I am not sure why you mentioned Dec 31, 2016. Did you mean Jan 1, 2017?