Canada's position was that after helping Britain to fight in WWI and sacrificing many soldiers for the cause, they deserved much more of a say over the running of their own country. They pushed Britain for this. It became especially pressing after the 1926 King-Byng affair (a personal favourite of mine from Canadian history), in which the Governor General of Canada - Julien Byng, refused to dissolve parliament when the prime minister William Lyon Mackenzie King requested. Basically, the Governor General was supposed to be a figurehead, but acted as though he had real power to shape the Canadian government. So Canada demanded clarification from Britain about its legal position. British parlimentarian and former PM Balfour issued the 1926 Balfour Report, which recognized the essentially equal legal status of Britain and the Dominions (Canada, Australia, NZ, etc). There was a period of negotiations, and then the 1931 Statue of Westminster was passed in British parliament, cementing the independence of Canada's government. A few items remained under British control, or were simply phased out slowly. The British Privy Council remained the highest court in Canada until 1949, for instance. Canada also remained unable to make any changes to its constitution without British permission, which is what eventually prompted the 1982 Charter of Rights and Freedoms- it was about taking the Canadian constitution out of the hands of the British and gaining full control over the (mostly) final bits of Canadian autonomy. So Canada was an independent country in basically every meaningful way long before 1982. I think most people would say as of 1931? Though ties remained strong to Britain even after that, obviously. This does not necessarily explain Canadian immigration policy, but I hope this can help to place Canadian governance in the twentieth century into context. I also hope someone is willing to step in and talk about immigration laws, as they are not my strong suit. Sources: Every year of mandatory Canadian history in our school system ever; but seriously- http://www.thecanadianencyclopedia.ca/en/article/canadian-charter-of-rights-and-freedoms/

• the same encyclopedia has articles on the King-Byng Crisis, the Statute of Westminster etc.