When using any of Canada Post's Canadian mail products, the return address on the mailing piece must be a valid Canadian address. Of course, we are referring to the return address on the envelope or self-mailer. If brochures, flyers etc. are stuffed into envelopes, the mailer can use whatever address they wish on the brochures or flyers (since only the recipients will see the address). When U.S. or foreign businesses send out direct mailings in Canada, they normally use a Canadian mail service provider to prepare the mailing for them. In this case, they frequently use the mail service provider's address as the return address.