The word "renounced" really seems to confuse a lot of people. The U.S. did NOT require an applicant for naturalization to renounce their Canadian citizenship to Canadian authorities. What they required is that the applicant renounce foreign loyalties as part of the U.S. naturalization process, i.e. to U.S. authorities. That kind of renunciation DID matter, up until 1977. However, as of April 17, 2009 (or 2015 for those who lost British subject status before 1947), those renunciations made to U.S. (or other foreign) authorities by Canadians before 1977 are ignored.
There is a 99.9% chance that your husband is a Canadian citizen.