Is this a good use for the canonical tag?

Marketing
1

The client has his website hosted on his main domain. Then for each service he offers, he has a keyword-rich domain pointing to the relevant page on the main domain website, so:

www.service1.com points to www.maindomain.com/service1
www.service2.com points to www.maindomain.com/service2

etc… These are cloaked redirects so the user only ever sees www.service2.com in their address bar.

Ive just been looking in Google WMT and see that on the Crawl errors screen (there a few crawl errors that need cleaning up) that it lists:

www.maindomain.com/service1
www.service1.com
service1.com
www.service2.com
service2.com

etc… So it seems like Google is treating all the above as seperate pages - but they are actually all just pointing to one page. Im concerned about being penalised for duplicate content. Should I use the canonical tag like this?

<link rel=“canonical” href=“www.maindomain.com/service1” />

Is that a good use of the canonical tag? Im slightly concerned to use it because www.service1.com is getting good rankings and I dont want to harm those.

As a bonus question, should I also add www.service1.com to Google WMT and set it to use the www version of the domain? This is just a domain ref pointing to www.maindomain.com/service1 , so is it worth adding to Google WMT?

Sorry about the long winded post, I hope it makes sense.

2

What that will do is tell Google to use that form of the URL - which might not be the actual URL itself, but can be an alternative more user-friendly route to it.

3

I’m looking to not get penalised for dupe content. So it looks like this is the solution I need to use. As long as www.service1.com ranking arent affected(?).