Do you need to use canonicals on a subdomain if...

[nickajankowski]

Ok so I just began working on a site that situation is something like this:

Product pages can be found by seaching either:
https://shop.example.com/Products/List.aspx?c=5&t=146
OR
https://www.example.com/Products/List.aspx?c=5&t=146

I found the second variation only by doing a crawl with Screaming Frog SEO Spider; there aren't any links to it on the internal pages. Everything points to the subdomain shop.example.com

My question is: is this a situation where I need to create a canonical link? Do the SEs view subdomains as duplicate content? I feel like this is an obvious answer and I'm overthinking it.

[SilverMoon]

Although google is smart enough to pickup only 1 url and ignore the rest without hurting the site's seo, still this should be fixed.

There should only be 1 domain hosting the contents.

Canonical tags are used to indicate the primary page out of a set of pages.
For example if you have 1 large article split into 5 pages, the first page should be canonical.

It is not supposed to be used to indicate the primary domain or anything such.