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You can have a page canonical to itself, so if you just add the canonical tags to all the pages, they'll appear on all of masked domains as well. Thomas is right; if your goal is to get any of the vanity domains on search result pages, the canonical tags will prevent that.  A better set up might be to have the home pages be different (with the reps name and information), and then have the rest of the pages on the site be duplicate content with canonical tags.  To say the sites do not exist isn't really accurate... it just means you haven't set them up yet.