我係香港人，但擁有加拿大護照，10年前回流香港，但因當時加拿大有物業所以並沒有申請 non-resident，但沒有申報海外資產. 現在加拿大物業已出售，若我想申請non-resident , 會唔會有咩稅務問題呢?

Changing to nonresident for tax purpose is not an issue (as you have been eligible for a while). Your only problem is CTA may have a problem with your non-reporting of foreign assets.

As a tax resident, you have the obligation to report your foreign assets (nonresidents are exempted). So your failure to file, if found, could make you subject to a heavy fine.