Choose an editor you trustThe most important thing is to choose an editor you trust and feel comfortable with. Your editor is bound by professional ethics to respect your privacy and your ownership of the manuscript. Make sure the person you’re thinking of hiring is a legitimate practitioner. Do an online search for their name and contact information and make sure their information checks out. Make sure their communications with you sound reasonable. You can also discuss the work on the phone, ask for references, see if the editor’s LinkedIn connections look believable, and find out if they belong to a professional organization.
Put your expectations in writingAlthough a good editor will respect your ownership rights, there’s no harm in writing a simple letter of agreement or contract that states that the editor cannot share the manuscript with any third party without your explicit permission and that you retain full rights. Editors Canada has a sample editing contract that you could add this to.
Use good computer securityAs well as taking precautions to make sure you don’t lose your work to a computer crash, you should also consider computer security. If you are very concerned about security, consider encrypting your manuscript before you store it in a cloud storage service or send it via email.
Understand that you already have copyright protectionIt’s important to understand that under Canadian and U.S. law,* you automatically have copyright on your manuscript as soon as your work is written down. Although you can register your work with the Copyright Board of Canada, you don’t need to do that to secure your rights. (If you do decide to register your work, it probably makes more sense to register at the time that you publish, when the manuscript is in its final form and you are releasing it into the wild.)
*In all countries that are members of the Berne Convention, copyright comes into being automatically, without the creator having to register their work.