From Open Canada, we see why CANZUK is a failure of middle power imagination:

The answer for Haass (as it is for Judah) is leadership. But middle power leadership is not the same as great power leadership. Middle power leadership cannot trade in vague (if lofty) ambitions or general concepts. To be effective, middle powers must be focused, detail-orientated and technically proficient. This was the approach Canada used to lead on peacekeeping, organizing the Montreal Protocol on ozone-depleting chemicals, the Ottawa Convention on anti-personnel landmines and the Responsibly to Protect. All of these were clear-eyed, focused attempts to improve the international system. By leveraging their technical acumen and accumulated diplomatic capital, Canada and other middle powers got things done. These successes built international reputations and skills that could then be applied to parochial state interests. CANZUK’s supporters do not have this focus. Instead, facing complex problems, they offer vague gestures to shared liberal values.

This is probably the most direct explanation of why middle powers, as often considered amongst the Anglosphere, are routinely unable to actually achieve their goals or stated objectives. Dangerously, states and their foreign ministers may enter into arrangements in the hopes that doing so will re-create a past golden age only to realize, years later, that looking backwards has caused their respective nations to further fail to take hold of their individual and collective futures in the world stage.

While building alliances and tightening friendships can be helpful, they must be accompanied with clear and specific areas of policy coordination. Doing anything else will not enable middle powers to exert substantial power on the world stage.