It's not that uncommon. You would go about this like any other couple planning to get married: go to city hall or equivalent for a marriage licence (check what identification needed), book a time/make arrangements with someone with the permission to officiate at marriages (many city halls will have some recommendations and/or space, or many/most religious organisations do), get the marriage done (witnesses etc as needed), wait for the marriage certificate (varies by province and possibly delays in covid time, perhaps four to eight weeks?). Note documentation requirements may be more demanding if either of you has been divorced.
Note: saying this with NO information on whether it will resolve your spouse's status issues.