Are you saying that you have already submitted your application to Mississauga? If so, you should contact Mississauga asap and ask to have the application withdrawn.
If they process the application, this could put your husband's PR status in jeopardy due to misrepresentation (i.e. lying about his status). When he filed the application for his own PR he declared himself as single - and he re-confirmed that he was single when he landed in Canada as a PR and didn't declare any changes to his family composition. Since he was actually common-law with you this entire time, he misrepresented his status as single and there's a chance CIC could revoke his PR status for this.
If they process the application, this could put your husband's PR status in jeopardy due to misrepresentation (i.e. lying about his status). When he filed the application for his own PR he declared himself as single - and he re-confirmed that he was single when he landed in Canada as a PR and didn't declare any changes to his family composition. Since he was actually common-law with you this entire time, he misrepresented his status as single and there's a chance CIC could revoke his PR status for this.