Your uncle and his family cannot apply directly for Canadian citizenship, but if he is planning to emigrate to Canada and if he meets the other requirements of the relevant points based system (Express Entry, etc), he will get extra points (about 15 out of a possible 1200 points, so not that many) if he has a sibling living in Canada.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.