[Docere]

Yeah, Greek language retention is higher than Italian in both countries.

One hypothesis is that the Greek Orthodox Church plays a role in supporting "Greekness." Meanwhile, with regard to Italians, while the RC Church may be based in Rome, it isn't "their" church.

Another is more recent immigration of Greeks, at least in Canada. Postwar Greek immigration was on average a decade later than Italian (Italian was more 50s/60s while postwar Greek was more 60s/70s). Canada also has a sizable pre-war Italian community (less than the US but more proportionately and numerically important than Australia), but Greek Canadians are almost all post-war.