Definitely worth trying... Embassies are there to help citizens (PRs are another story).

And as has been stated, Canada can’t deny you entry but without proof you may be there some time. As long as you enter the US with the ESTA and tell them you are staying there for a day and then going up to Canada they really shouldn’t care more. It’s a fine line between telling the truth and omitting the fact that you plan to try and enter Canada as a citizen without proof.

To be honest, it may be worth consulting an attorney about this who can likely give you much better advice. Likely for a cost, but for peace of mind is a few hours and some $$$ worth it? They may even tell you what your options are as a free evaluation?

Theres also a free forum not on FT setup for Canadian immigration and citizenship that may be able to provide threads specific to your situation and/or people who have been in a very similar situation. I can try and dig it out if helpful.

Oh and people fly into the US instead of Canada all the time as it tends to save significant money. Flying into and around Canada is much more expensive thanks to a lack of airlines and other factors. Of course, if you don’t have a return ticket from Canada or the US back to Australia that may raise a large red flag.