When your husband receives his COPR, there will be an expiration date on it. He must land in Canada on or before that expiration date. It is usually tied to his medical exam expiration date. If he is close to expiration when they get ready to issue his visa, they can either opt to extend his medical results (usually for 1 year) or they can request a new medical be done in order to issue the visa. That really all depends on the VO processing the application.