a) Is Canada and Mexico affecting or is somehow responsible for the disastrous way that the US is handling COVID-19 ? Otherwise it’s a moot point.
b) Number of international travellers is irrelevant given that the policy in Australia was to quarantine ALL visitors for 14 days. Same policy that the UK has now adopted and you can’t argue that they don’t have a lot of international travellers. Again it is simply bad policy.
c) Climate is not that different to many parts of the US right now. It’s not like it’s winter versus summer. Fairly mild temperatures in both countries right now.