SiredBlood has rules for a combined UK economy that work pretty well; basically there is a 20 IPC/turn spending cap in India, and otherwise you just combine the entire UK + Canada + India + South Africa into one economy, with ANZAC remaining separate. If you don’t like the 20 IPC/turn rule, you could replace the major IC in India with a pair of minor ICs, one in India and one in West India.
ANZAC is interesting as a separate power because ( a ) they have a core cluster of facilities & 2-IPC territories of Queensland, New South Wales, and New Zealand that are far enough away from Japan to be defensible, ( b ) they have economic interests like Java and New Guinea that are close enough to Japan to make for immediate conflict, ( c ) they can realistically get up to 20+ IPCs in many games, which gives them options beyond just sitting and turtling, and ( d ) they are a convenient ‘junior partner’ for the US Pacific Navy, which allows them to punch above their weight.
None of these are true for Canada except for ( a ). It’s easy to defend Ontario and Quebec, but Canada doesn’t have any economic interests that put them into immediate conflict with any Axis powers, they have no realistic path to get to 20+ IPCs, and the British Atlantic navy isn’t strong enough in this version of the game to need or want a junior partner. It might be possible to radically adjust the starting setup so that the English-speaking countries have a larger total Atlantic navy that is split up less favorably among UK & Canada so as to preserve roughly the same level of power, or to have a larger Canadian navy that serves as a sort of Allied bid, but you can’t just split Canada off as its own power without tilting the power balance further in favor of the Axis. Even if you do fix the balance issue, it’s not obvious that Canada is a strategically interesting power on this map. I am very pro-Canada and have great respect for Canada’s historical wartime contributions, and I think thematically it would be a lot of fun to play a Canadian power, but I don’t think it’s a realistic goal mechanically for this map and setup.