Is there a way to forward banklink benefits from one domain to another without a redirect?

[OCN]

In this situation I have SiteA, and SiteB on completely separate domains.  SiteA is the marketing front for the company and SiteB is an app that company owns.  SiteB receives a fair amount of backlinks as it has the login page of the application where customers link to a branded version for their members to login. Additionally none of that domain is indexable including the login page. SiteB's domain can't be changed to be a subdomain of SiteA as it isn't technically feasible.

Initially I was reluctant to use canonical because as it isn't really duplicate content.  Is there a method for forwarding any link-juice from SiteB to SiteA without the use of a redirect and would canonical be appropriate in this case?  Additionally would SiteB's not being indexed negate any link benefit?

Edit: Typo

[ClaytonJ]

Identifying a canonical URL for each range of comparable URLs can enhance the SEO of both sites. This is as the search engine knows which version is canonical, so it can consider the links pointing at all the different versions as links to the canonical version.

Setting a canonical is similar in concept to a 301 redirect, only without actually redirecting.

So the best outcome based on the above query is canonical.  I note that google on occasions does choose to ignore canonicals.  But it sounds like your starting point.

[OCN]

The two pages in question here don't contain the same content.  SiteA is a marketing description and features of the product and SiteB would be a login page for that product.  Would the lack of duplicate content cause an issue?

[ClaytonJ]

Possibly as Google may ignore the canonical - however, if the money site is the one you are pointing to, it is worth doing.  It does sound like a disconnect, as would expect both features to be on same site  - assume a "buy now" - CTA and click onto a separate site has also been considered..

[effectdigital]

Canonical tags avoid duplicate content and help to determine page relevance, but common current SEO thinking is that they do not pass link equity or SEO authority. If they do, it's not much - and not comparable to the power of a 'properly' set up 301 redirect

Even when you DO use 301 redirects, they can fail for loads of different reasons. One big reason is content similarity in machine terms (think Boolean string similarity, for the content of the old and new URLs)

If even the mighty 301 has so many stipulations where it can just 'stop working' (or never work in the first place) I'd be highly, highly skeptical that canonical tags would have the desired effect

[effectdigital]

Yes it's highly likely the canonical would be ignored. Regardless, canonical tags are NOT commonly thought to pass SEO authority (only relevance and content duplication nullification)

[OCN]

In this case where I'm unable to do any sort of 301 is there any other in-page options that might be a reliable way to forward link equity?

The other option is that I keep pressing to change the domain of the login page to a subdomain of the marketing site, which is unlikely at this point, but even in that case the subdomain would cause issues with link equity correct?