I am very biased as I am Canadian and have lived in Canada my whole life. However, my wife is Australian and I have visited many times. We have looked into moving there and the only thing that really stops us is our pets due to the significant quarantine requirements.
I would say Canada's tech sector is larger, mostly because of our proximity to the States but Australia has a very large and vibrant tech sector; like most places, mostly found in the major cities: Sydney and Melbourne. When I have looked for work there I have found no shortage of jobs opportunities. However, I have not looked during this most recent economic recession.
Do you plan to become a citizen? If so you may consider the politics of each country. In the grand, Canada is more liberal whereas Australia is more conservative. However, both offer significant social services.
Do you plan to travel? Asia is closer to Australia, with Tokyo being nearly equidistant between Sydney and Vancouver. Europe is closer to Canada, especially Eastern Canada where many major/prominent Universities are located (I went to school on the West Coast so I don't endorse those schools).
Do you plan on working in the States? I really don't know about how this works from an Australian perspective but US based companies have had no issues with my Canadian education and current place of residence (Canada and the US allow for fairly easy migration of professionals through our free trade agreements). I would assume Australia has similar, if not identical, standing but this may need further investigation.
What matters to you in your life? I think you would be equally happy regarding education and work opportunities so I would look at other priorities.