Howard had some pretty nasty things to say about Canada when he first came on the air in Montreal and Toronto, leading to his almost immediately being put off the air in Montreal. Howard's long stated hatred of everything French (including Celine Dion) is legendary - "Toulouse-Lautrec is a troll", "the Eiffel Tower is ugly", "occupied France worked harder for the Germans than the native Germans did" - all quotes from Howard. This attitude and the statements he made in the press conference during his initial airing in Canada sparked a feud between Howard and some Canadian officials. This is probably why our neighbors to the north will not be hearing him on the Sirius Canada stations.
If you are in Canada and want to hear Stern, all you have to do is buy your equiptment from the US. Many people are doing it and they can now receive Howard's channels with no problems.