Can a refugee go back to his country after getting citizenship?
According to Geneva Convention Refugee Act a host country can take back their citizenship or PR if the former refugee ever go back country he fled from, Scandinavian countries use that article to strip citizenship and PR and turn them away at point of entry.
Canada allows refugees to return to their home countries after citizenship. It's not an issue in Canada.
However returning to the home country pre-citizenship (while still a PR) can certainly be an issue and can trigger revocation of PR status.
Once someone is a citizen and has a Canadian passport, they are good to go.