If I could clarify, for any individuals not residing in Canada or who are not present in Canada, the summons would have no force. The committee's powers and privileges are limited to the physical borders of Canada. If anybody is elsewhere on the planet, our summons has little to no effect.
If they are in Canada and they receive the summons and do not appear, the committee can report that matter to the House. Then it would be up to the House to decide if that is contempt. If it is contempt, someone would move an appropriate remedy: maybe call the person to the House or have the Sergeant-at-Arms send a bailiff to get them. If a person ignores a summons, it's completely up to the House to deal with it. The committee would have to report it first, and then the House would deal with it.