Originally Posted by
JimInOhio
I don't see how the airlines would know the OP is a dual-citizen if he/she only has an Australia passport and never had a Canada passport.
Be careful of the advice you are giving.
For OP to travel to Canada illegally on an Australian passport, he will require an eTA from Canada. But, Canadian law requires him to travel to Canada on his Canadian passport.
So, either he makes false statements to Canada in order to obtain an eTA so that he is permitted to board, both in Australia and in the US, and then asserts to Canada that he is Canadian on arrival in Canada or he advises that he is a Canadian national and is required by the air carriers both departing Australia and the US (if he gets that far) to produce a Canadian passport.
This isn't one of these tall tales which people tell to get out from under a change fee. It can have real consequences for OP.