AOR is usually sent by email. Occasionally it is sent by letter, even to applicants who provided an email address.
Other requests may arrive by mail (such as requests for proof of presence) relatively soon after AOR. Usually there is a delay between AOR and test/interview invitation, but time frames vary wildly.
You are allowed to travel, of course, but you are also expected to be able to respond to requests for additional information within a reasonable time (or your application can be considered abandoned), so it'll depend on how long you plan to go travelling. If you're going for a week or two you should be fine; if you're travelling for much longer than that you'll need to make sure someone trustworthy keeps an eye on your mailbox, and check your email while travelling. In that case you should also make sure you can come back to Canada in case you need to attend the test+interview, or if you're asked to send proof of presence (so you can gather the information they request).
