At the time of WW1 both Australia and Canada were quite small countries population wise but they contributed a greatly disproportionate amount of forces to fight in Europe and as a regard they lost a very high amount of soldiers, something on the order of over 1% of their total populations lost.
I know there were of course deep ties to the UK however these two nations were really under no physical risk of danger from Germany. It's hard to picture how at a certain point that fact wouldn't take precedence over the amount soldiers being sent out and lost?
Keep in mind Australia was still part of the British Empire at the time. They became a federation a decade or two earlier, but they were still compelled into the war constitutionally and because most of them were British in origin anyway, surprisingly enthusiastic to help the mother country.
Canada started volunteering and eventually tried conscription with mixed success - many were against war altogether, but the English / French tensions specifically ran high because of mixed nationalism and resulted in the Quebec Easter Riots (which were some of the worst in Canadian history)