Two URLs with same content

[BluespaceCreative]

We recently had a client who own multiple brands switch from having multiple urls to having a single domain with multiple sub domains. I've posted an example below to better explain.

My question is the original url is still functional, so there are two urls with identical content, yet I haven't been getting a duplicate content error. Also, would a rel canonical link be beneficial in this case since the duplicate content is on two separate domains?

My thoughts were to put a 301 redirect on the original pages so they permanently forward to the new sub-domain format. Is this the best course of action? If not, what would you recommend?

Example:

Original URLs
www.example1.com
www.example2.com
www.example3.com
www.parentcompany.com

New URLs
example1.parentcompany.com
example2.parentcompany.com
example3.parentcompany.com
www.parentcompany.com

Let me know if this I need to clarify anything in better detail.
Thanks in advance!

[JoeAmadon]

A 301 redirect is the best solution as it will point users and bots to what will then be the only source of the content. A rel="Canonical" will tell search engines which page is the canonical version but you will still have users hitting pages on the old domain and potential creating links to those pages instead of to your new subdomains, which isn't ideal.

[mozalbin]

I would prefer 301 before canonical. This is because you don't loose as much link juice/pagerank when using 301 as you are when using canonical. In this scenario, it's best to act like Matt Cutts says in the attached video.

Take a look at the vid' and please don't hesitate to ask further questions to me

watch?v=zW5UL3lzBOA