Australia's description as Anglo-Celtic references the disproportionately high proportion of its population who have Irish or Scots ancestry; around 23% versus the 44% who have English roots. On the other hand the proportion of its people who have "British" roots has been falling steadily for years. Some 18% currently hail from other parts of Europe (Germans and Italians contributing almost 7%). In addition some 5% now hail from SE Asia and China. I don't have up to data for Canada but I would suggest the position there is quite similar.
In the USA. however, it will depend very much on what you include in the "white" category. A very much higher percentage in the States is Hispanic, plus there was widespread immigration from Eastern Europe and Russia, both Jewish and non-Jewish. A large percentage of the original population at the time of US Independence were of German and Dutch stock. After all this time people may have quite personal views of their orogins which may or may not truly reflect their genetic heritage.