The term canonical domain denotes the preferred domain for your website. This is an important consideration when visitors can access your site by using multiple domains. Even though the majority of people understand that http://www.mysite.com and http://mysite.com are the same website, a search engine sees these as two different websites. That is why it is important to let the search engines know which is the preferred domain for accessing your site.
The WWW domain is no better than the non-WWW domain where SEO is concerned. The important thing is to choose one or the other and be consistent with it throughout your site. That means, if you choose to use the non-www domain then any absolute links to other pages on your site should use the non-www domain. Relative links automatically use the non-www domain.
When you have multiple CNAME records for your domain, you can use the Domains subtab on the Web Site Setup record to specify the primary URL and and also define any alias records so that all aliases that a visitor might use to access your site are redirected to the primary URL of your site. Additionally, search engines see this as a 301 redirect for any aliases to the primary URL for your site.
To set the canonical domain for your site:
Go to Setup > SuiteCommerce Advanced > Set Up Web sites.
Click the edit link for the website for which you need to establish a canonical domain.
Select the Domain subtab.
In the list of Domains, locate your primary domain.
In the Primary Web Site URL column for your primary domain, check the box to indicate that this is the primary domain for the site.
Enter a new record in the table for each domain alias for which you have a CNAME record.
Any domain alias you enter here must have a corresponding CNAME DNS record defined with your domain provider.
When visitors or search engines access your site with any of the domain aliases that you specify here, they are automatically redirected to the URL that you have marked as the primary website URL.