I ignore if this surname is largely spread around french Canada. In France it is at rank 1277 among the french surnames(see the site "Carte de France de Votre Nom de Famille").
According to Jean TOSTI this surname could come from a name of a place:DION spread in some french regions.
Or also from the first name DIDON which is derived from an old germanic first name (see the site:
www.jtosti.com/noms).
As in Canada, Dion is very popular in Europe too because of the singer Céline Dion.