All of you know what a canonical does, right? It basically is a 301 redirect designed for spiders only - more on that over here. But many of you do not know about the isSimilarTo schema. As defined by schema.org, it is a pointer to another, functionally similar product (or multiple products).
One webmaster asked John Mueller of Google if it is treated by Google the same as Google treats a canonical. The answer is no.
Here are the tweets:
@cremf A rel=canonical is an indexing signal (which equivalent URL do you prefer?), I wouldn't compare that to isSimilarTo structured data.— John Mueller (@JohnMu) March 29, 2016
So they are not really similar at all. Good question, never seen it before.
Forum discussion at Twitter.