This is a very complex issue, and there is no universal answer. I had to deal with it several times. For example, if a book is in the public domain in one country and still under the copyright in another, you may be liable in that country if you allow a user from that country to download it. In practice, however, it is extremely rare that anyone tries to enforce such laws.
I would recommend that you comply with both the U.S. and Canadian laws, since you may be deemed to have a physical presence (nexus) in both countries. As a minimum, you may ask your users to certify, when they sign up, which country they are from and that they are not aware of any laws that prevent them from using your service. I don't think there is any law that actually requires you to verify their representations, but you may want to consult with an attorney about that. -- You received this message because you are subscribed to the Google Groups "Google App Engine" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/google-appengine. For more options, visit https://groups.google.com/groups/opt_out.
