The Master Surname Index (not online) (mostly burials in Alberta cemeteries) of the Alberta Genealogical Society does not lists your Gerald JOHNSON;
Nor does the online Medicine Hat cemetery. You can do a Google Search for "Medicine Hat Cemetery" and click on Burial Listing or Contact.
There are no online Marriages. You will have to contact the Alberta Vital Statistics at Edmonton
For further research please contact the AGS Medicine Hat Branch or the Research Services Committee of the Edmonton Branch,
http://abgensoc.ca/ The Edmonton Branch
http://agsedm.edmonton.ab.caPeter