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It's probably easier to only use 301 redirects, especially if the majority of deleted posts are not going to be restored and are deleted permanently in a few months.

No problem. You can edit the canonical links through Yoast's SEO plugin, just go into the page/post and then navigate to the 'advanced' tab within Yoast - you can then set the custom canonical link. Regarding your links that point to you with no trailing slash, WP automatically redirects any URLs without a trailing slash to one with one - this will then flow the PageRank into the correct URL, so don't worry.

There is my .htaccess at the moment: <ifmodule mod_rewrite.c="">RewriteEngine On RewriteBase / RewriteRule ^index.php$ - [L] RewriteCond %{REQUEST_FILENAME} !-f RewriteCond %{REQUEST_FILENAME} !-d RewriteRule . /index.php [L]</ifmodule> I don't want to mess with it because I don't have an access to cpanel.

That sucks.  I suspect the site is not configured properly, but that it would require cpanel\ftp access to fix properly. At least you have a solution, which is half the battle with Wordpress.  There are always bugs that need to be worked around (mainly from theme problems in my experience). Anyway, glad you got a solution.

https://www.phpbb.com/community/viewtopic.php?p=12896544

Hey Thomas - thanks for jumping in! Just to clarify; Yoast will allow you to noindex categories - I'm sure that's what you meant. You can delete categories in the default WP setup. And I think you mean "noindex all subpages of archives"