I think Canada as a separate power is unnecessary. I’m not too thrilled with ANZAC as a separate power, but I think I know why the designers did it: 1.) play balance, and 2.) historical accuracy.
Right now, Japan has to face 3 weak powers (Commonwealth, China, and ANZAC) and one strong power (US). If Commonwealth and ANZAC were allowed to act as one unit, they could pool their forces and attack together. I don’t think that would affect play balance very much. It’s also NOT historically accurate to keep them separate. ANZAC, British, Indian, South African, Rhodesian, and Canadian troops worked together in joint commands frequently, particularly in North Africa. And, colonial griping about “those arrogant Pommies” aside, they generally worked quite well together.
But allowing ANZAC and Commonwealth to pool their income would mean Australia and India could build bombers, battleships, and aircraft carriers, which would not be historically accurate. Also, allowing ANZAC income to be spent in India would allow them to crank out large numbers of infantry and tanks. Again, not historically accurate. Yes, India had a huge population, but that doesn’t equate to being able to build a huge army overnight. India had a fair amount of industrial capacity, but not for building capital ships, combat aircraft, and tanks. And the technical expertise needed for expanding such activities was concentrated in Britain and Canada. Also, large numbers if Indian troops were committed to North Africa, Sicily, and Italy. And India was a huge country at that time, and included Pakistan, Bangledesh, Ceylon (Sri Lanka), and, I believe, parts of Afghanistan. Much of the Indian army was committed to keeping the peace and discouraging rebellions among the various factions, and would therefore not be available to commit to the fight against Japan.
Now, for my own house rules, I plan to have Britain, ANZAC, and Free French forces be combined in a single turn. They can operate together for combat purposes, but have to keep their incomes separate. ANZAC income can only be spent in ANZAC factories. Commonwealth income can only be spent in Commonwealth factories (Britain, Canada, India, South Africa, and any new factories built in Commonwealth controlled territory). I think I’ll allow Free French (I’m lumping Dutch and Belgians in with them) to use the income from their colonies to build units in British factories.