AFAIK....Mrs. Cruz NEVER renounced her American citizenship, but I may be wrong. Was she a Canadian naturalized citizen?
It hasn’t been clarified but her Canadian Citizenship papers or passport application should say. Canadian law as I understand it was changed in the ‘70’s to allow for dual citizenship but probably wouldn’t have when Cruz was born.
Even if his mother wasn’t a naturalized Canadian she may still have had to apply for American citizenship for kids born there. He needs to hold a press conference and get it all out at once.