I think there is a better case to be made for honourary then for riddum Honourary has a much higher occurrence on google is not pronounce different and is used in academia and government I personally feel that riddum would be considered by most to be slang while honourary would be more a variant  I think that in a dispute over whether it is a variant we should error on the side of accepting the variant provided sources can be found In general I would agree with correcting it to honorary unless its a Canada article and the sources use honourary In that case I think the article should go with the predominately sourced one except in the case of a direct quote