Both countries are roughly equal in standards of living. Canada’s economy is larger, but you are not buying the entire country. Some jobs in Australia pay more than the same jobs in Canada. Some jobs in Canada pay more than the same jobs in Australia. You must compare job salaries for which you are qualified. Canada has somewhat better social programs, but you are not immigrating to access welfare programs. Australia has a better equipped military, but neither are under threat of war. Canada has extremes of cold, but Australia has extremes of heat. Both are actually pleasant enough to live in. Canada has better access to the US and Europe, but Australia has better access to Asia. Will you be able to get a job? Again, difficult to say. The job market in Canada is larger, but then, it can be harder to obtain work at your previous level in Canada. Many variables depend on individual circumstance. Larger cities see the majority of immigrants, so many compete with each other. In smaller cities (or towns) there is less competition, but the opportunities may be less.
Can I actually immigrate to either? Will either actually let you come? Immigration to both is highly competitive and skills which allow you into one, may be less helpful in the other. Will my choice be simply limited by my ability to immigrate. Are there disqualifiers? Both countries have specific issues which will bar you from entry. Would anyone in the family be disqualified from entry? Will your children be safe and be afforded opportunity? Yes in both countries, but to different levels in different parts of each country. If you are comparing living in Onslow, Western Australia to Cape Dorset, Nunavut, the equations change dramatically from comparing Melbourne or Sydney to Toronto or Vancouver. What will transition be like? Again, support for immigrants varies more by city rather than by country.