This legislation, passed by the British Parliament, created Canada as a new, domestically self-governing federation, consisting of the provinces of New Brunswick, Nova Scotia, Ontario and Quebec, on July 1, 1867. The British North America Act (now the Constitution Act) established the new federation’s distribution of responsibilities and powers for each level of government and the rights of its inhabitants. The BNA Act, as it is often known, was both Canada’s greatest strength and its greatest challenge: it created an enduring federation that matured into a peaceful, prosperous and well-governed state, while challenging successive governments to alter its amending formula and distribution of powers to meet the needs of its inhabitants. In particular, early attempts to involve the federal government in the delivery of social services, such as health care, failed because the BNA Act made health care a provincial responsibility. Gradually, the federal and provincial governments reached a compromise within the limits of the BNA Act wherein provinces, supported by federal grants, would provide a national standard of health care. By necessitating a federal–provincial compromise, the BNA Act contributed to medicare’s evolution as a government-funded, provincially delivered national social welfare program."
Source: Canadian Museum of History