With rel next/previous you ask Google to consider all the pages with these tags to be considered as one page
With a canonical you indicate that the page is a duplicate (or variation) of the canonical url.

Your developers are right - if you put the first page as canonical for the subsequent pages your are basically asking Google to ignore the 2nd, 3rd,... pages which is in conflict with rel next/previous.

It is possible to combine both canonical & rel next/previous - but not in the way as your SEO company is suggesting. Example from Google:

The canonical in this case is used to strip the sessionid which could be a cause for duplicate content.

Please not that if your category pages are split over a lot of pages (like 100) - the rel / next previous stops making sense. In that case it's probably better to focus on optimising the first page & put a "noindex/follow" on the subsequent pages.

Dirk

You could add them to the robots.txt but it you have to remember that Google will only read the first 500kb (source) - as far as I understand with the number of url's you want to block you'll pass this limit.

As Google bot is able to understand basic regex expressions it's probably better to use regex (you will probably be able to block all these url's with a few lines of code.
More info here  & on Moz: https://moz.com/blog/interactive-guide-to-robots-txt

Dirk

To be very honest I don't think it will make a difference if it's going to the /us/ version rather than the root.

If you prefer - you could keep the us version on the root & only redirect the non-us visitors to a country version.

Dirk

As far as I understand there is no content on domain.com so your last line makes no sense.

If you want the default version to be the us version you should put

Don't forget that hreflang needs to be placed on every page of your site - you can check if the implementation is correct here: http://flang.dejanseo.com.au/

Dirk

Be careful when redirecting based on ip - you have to make sure that Googlebot (accessing your site with a Californian ip) can access the non-US versions. If you have a link on each page to change the version to another country (and these pages are accessible without being redirected) you should be ok.

An alternative to ip based redirection is to use your main domain for a country select page and to store the selection in a cookie - so you can redirect to the chosen version on subsequent visits. Check volvocars.com as an example. The advantage is of this method is that you give control to the user (I personally find it quite annoying when I'm being redirected to the local version when I'm abroad and want to visit my "home" version).

rgds,

Dirk

Don't forget that . & ? have a specific meaning within regex - if you want to use them for pattern matching you will have to escape them. Also be aware that not all bots are capable of interpreting regex in robots.txt - you might want to be more explicit on the user agent - only using regex for Google bot.

User-agent: Googlebot

#disallowing page.php and any parameters after it

disallow: /page.php

#but leaving anything that starts with par1=ABC

allow: page.php?par1=ABC

Dirk

Hi,

The difference between them

• canonical : url has a canonical url - which can be self-referencing (canonical url = url) or not

• canonicalised: url has a canonical url which is not self-referencing (canonical url <> url)

• no canonical : quite obvious - the url has no canonical.

Potential issues could be - url's that you would like to have a canonical don't have a canonical or url's that are canonicalised don't have the right canonical url. You can use the lists (both canonicalised & no canonical) from Screaming Frog to check them - but it's up to you to judge whether the canonical is ok or not (no automated tool can guess what your intentions are).
Typical mistakes with canonicals: all url's have the same canonical url (like the homepage), or have canonical url's that do not exist. You could also check this with Screaming Frog using the setting "respect canonicals" - this way only the canonical url's will be shown in the listing.

Also keep in mind that canonical url's are merely a friendly request to Google to index the canonical rather than the normal url - but it's not an obligation for Google to do this (check https://support.google.com/webmasters/answer/139066?hl=en quote: "the search results will be more likely to show users that URL structure. (Note: We attempt to respect this, but cannot guarantee this in all cases.)"

Dirk