Rel="canonical" and rel="alternate" both necessary?

[AlliedComputer]

We are fighting some duplicate content issues across multiple domains. We have a few magento stores that have different country codes. For example: domain.com and domain.ca, domain.com is the "main" domain.

We have set up different rel="alternative codes like:

The question is, do we need to add custom rel="canonical" tags to domain.ca that points to domain.com?

For example for domain.ca/product.html to point to:

Also how far does rel="canonical" follow?  For example if we have:
domain.ca/sub/product.html canonical to domain.com/sub/product.html
then,
domain.com/sub/product.html canonical to domain.com/product.html

[Dr-Pete]

I'm honestly not completely clear on what the different URLs are for - I'd just add a note to keep the core difference between canonical and 301s in mind. A canonical tag only impacts Google, and eventually, search results. A 301 impacts all visitors (and moves them to the other page). A lot of people get hung up on the SEO side, but the two methods are very different for end-users.

As Tom said, if these variations have no user value, you could consolidate them altogether with 301s. I always hesitate to suggest it without in-depth knowledge of the site, though, because I've seen people run off and do something dangerous.

[TomSlage]

What's the purpose of the URL if there's not even any sorting or anything unique going on? If's a sorted URL (say by "size" smallest-largest for /little leage/ URL) it might be actually useful to develop some unique category content to let the page rank separately.

If the content is totally unique, I don't think you could really go wrong redirecting. To be safe, I'd probably rely on analytics to answer the question "what impact will redirection have?" For instance, is there a difference in conversion rate between the URLs. If you see a conversion bump from a more specific URL, you might want to sleuth out what's causing it.

[AlliedComputer]

Would you worry about it if the categories are somewhat useful for users to drill down the content?

For example:
/product.html
/aluminum-baseball-bats/product.html
/little-league-baseball-bats/product.html

They don't sell bats but it is the easiest way to describe it I guess.  In this cause would you still 301 redirect the two longer urls to /product.html

[TomSlage]

Yes, providing that the /category1/ and /category2/ heirarchy doesn't help the user experience (e.g. product segmentation based on say, color and brand, which would be useful for users to drill down to).

I like 301s better because they are permanent, non-ambiguous, respected by all engines, and chiefly because they eliminate the possibilty of inlink dillution because the redirected URLs are never seeen.

[Dr-Pete]

Yeah, don't use rel=canonical for the same purpose as rel=alternate - the canonical tag will override the alternate/lang tag and may cause your alternate versions to rank incorrectly or not at all. It can be a bit unpredictable. If you only wanted one version to show up in search results, then rel=canonical would be ok, but rel=alternate is a softer signal to help Google rank the right page in the right situation. It's not perfect, but that's the intent.

As for multiple canonicals like what you described, that's essential like chaining 301-redirects. As much as possible, avoid it - you'll lose link equity, and Google may just not honor them in some cases. There's no hard/fast limit, and two levels may be ok in some cases, but I think it's just a recipe for trouble long-term. Fix the canonicals to be single-hop wherever possible.

[AlliedComputer]

Thanks that is what I was thinking, I just need to know more about if the bots will follow the canonical's past one level when pointing to a different domain and if so how many levels on the different sites.

[AlliedComputer]

Interesting idea, I might have to do that.  Right now I have canonical elements on the .com

It is a magento store so it creates dirty duplicate content when the products are in different categories out of the box, for example magento creates the following product pages:

domain.com/store/productcategory1/product.html
domain.com/store/productcategory2/product.html
domain.com/store/product.html

In this case I have canonical elements pointing the categories to the main root domain.com/store/product.html

So you think it would be better to do a 301 redirect for the different product urls that are in subcategories?

[TomSlage]

Miles,

On your last question, I'm wondering if those two canonical tags are necessary? Are the /sub/ versions of those pages necessary for user experience? If not, I'd add a canonical element to the .com version, then redirect the /sub/product.html to /product.html. That would help you avoid splitting link authority.

[FedeEinhorn]

Hey Miles,

The both are for different uses and may or may not be used in the same page depending on your situation.

If the content in the CA and COM versions is the same, then you should add a rel canonical + rel alternate, the rel alternate pointing to itself and the other version of it, and the canonical pointing to the one you consider definitive.

If the content isn't the same, then the rel canonical isn't needed (but suggested, pointing to itself in each lang/alternate), only the alternate should be in place.

You can read more on Dr. Pete's post here: http://a-moz.groupbuyseo.org/blog/rel-confused-answers-to-your-rel-canonical-questions

Hope that helps!