Getting the British Empire to acquire Hawaii and making it the Islands a Canadian Province during decolonization are two separate questions. As far the former question goes, maybe the US has a much worse relationship with Great Britain in the post-civil war period, or London doesn't get the Anglo-Japanese alliance to contain Russia at the same time as OTL, and Hawaii becomes a key way-station for the Royal Navy.
I could only see a Canadian Hawaii happening in some scenario where decolonization essentially means splitting up the colonies among the Dominions as subordinate territories or protectorates (like South Africa ruling Namibia in OTL), and Canada gets an extremely far-flung territory instead of Australia and New Zealand. If Hawaii ended up under British rule, the most plausible endgame is honestly some form of indirect colonial rule from London, and then Hawaiian independence. Why wouldn't London just keep the Hawaiian monarchy around as as part of an indirectly ruled protectorate kingdom (like Botswana or Lesotho) that eventually regains its independence?