An interesting question came up on Twitter.  Someone is ranking with identical pages across multiple sites and asked how best to tell Google they should be considered the same page, if it should be with noindex or via rel=canonical.

And according to Google, the answer is rel=canonical.

Illyes also confirms that using the rel=canonical method across multiple sites would not be seen as any kind of spam signal to Google.

It is interesting that an SEO wants to consolidate those pages when they own multiple top listings for the query across those different sites.  For many SEOs, this would be the dream, with owning sites all ranking at the top with the same content.

But it is possible that the site owner could have seen an algorithmic issue they suspect is at play, or a Google manual action, and they are now trying to fix it.  And they may want control of which site Google is choosing to display, since Google doesn’t always pick the one that is the “right” one according to the SEO, such as the primary brand one, or Google could be splitting it across different domains which could impact rankings as PageRank is diluted across the various pages on different sites.