Sure - he can apply for Canadian PR (if he qualifies to apply).
The overstay in Australia should not affect his application. However he needs to be honest about the dates of his stay in Australia when he completes the application for Canadian PR.
At the initial stage of the application it would not be an issue, but as the application progresses, he will need to provide Police Certificates from Australian authorities as long as he resided there after the age of 18....i'm not sure if austrailian authorities consider visa overstay as a "Crime" or not - your friend needs to find that out, if yes then it will appear on the Police certificate, & he would need to prepare a good justification if Canada officer asks for further details (thats my opinion). In general i think overstay alone is not a big deal, but if accompanied with an "arrest" for breaking the residency laws - or being deported as a result of overstay ..that can be an issue.
At the initial stage of the application it would not be an issue, but as the application progresses, he will need to provide Police Certificates from Australian authorities as long as he resided there after the age of 18....i'm not sure if austrailian authorities consider visa overstay as a "Crime" or not - your friend needs to find that out, if yes then it will appear on the Police certificate, & he would need to prepare a good justification if Canada officer asks for further details (thats my opinion). In general i think overstay alone is not a big deal, but if accompanied with an "arrest" for breaking the residency laws - or being deported as a result of overstay ..that can be an issue.