He cannot marry you before he comes to Canada and becomes a PR. If he does, he will no longer qualify as a his parents' dependent and will no longer qualify for PR under his parents' application. You cannot get married until after he comes to Canada and becomes a PR.
Once you are married, he can sponsor you for PR immediately. Note that he will have to be living in Canada when he sponsors you for PR and he will have to continue living in Canada while the application is being processed (he can take short trips of three weeks outside of Canada but must be living in Canada primarily while the application is being process).
You should read through the discussions in the Family Sponsorship section of the forum for more information.
