The legal issue is called "Dual Intent". A person applying for a visitor's visa who has been sponsored for PR has to prove that they will leave Canada at the end of their visit to the satisfaction of the visa officer. So they will look at the amount of time applied for, if there is a special reason, as well as all the other factors mentioned. So if there is a special event for your husband to attend like a family wedding and he is not applying for a 6 month visa, etc. Even then, still very difficult to get. Good luck.