Australians are not exactly a svelte lot either, ranking 10th in the OECD countries for obesity (US is the third), and on par with the UK.

Yeah, Ozzies also drink like fish, at least when I was living there. Good lord, so much boozing.

  less likely to die from drug overdoses. Older age groups are also less likely to die from chronic diseases such as circulatory problems and heart disease. Cancer mortality rates are lower in Australia than they are in all other Anglophone countries, except among American men aged over 65. And Australians are also less likely to die in road accidents than other countries

So why are they getting less chronic diseases despite being equally obese.

Obesity's definitely a factor, but other developed countries haven't seen the same level of stagnation despite their own skyrocketing obesity rates. For that matter, Americans also smoke less compared to most of Europe.

There's likely at least one other major factor, and I would assume that it's some variation of "inability to access high-quality care for financial reasons" given how much of a wealth disparity there is in various healthcare outcomes.

  Older age groups are also less likely to die from chronic diseases such as circulatory problems and heart disease. Cancer mortality rates are lower in Australia than they are in all other Anglophone countries 

So you get less cancer because you have 'access high quality healthcare' ? how does that work?

  wealth disparity there is in various healthcare outcomes.

Wealthy have access to good food. have less stress and engage in mental and physical recreation more and ofcourse regular screenings.

Why would it depend just on one factor like hospital access?

Cancer mortality is not the same as incidence, you can plausibly have more cancer while still having a lower mortality

Plausibly you can get less cancer by encouraging people to stop smoking, drink less, be less exposured to known carcinogens (either by awareness or regulation). A good healthcare system can also mean you catch cancers early or treat them earlier.