I am new to CakePHP and want an admin panel on my custom CMS for a client. Is there any way other than just linking to an admin page to each controller that I can pull views from other controllers such as users and posts?
Here is a great article on creating a admin section for CakePHP Creating an Admin Section with CakePHP
The better and cleaner way will be to put all your pages of admin under controllers. For example: controllers/admin
You can try PoundCake Control Panel. It is still in beta but may be useful.
The easiest and fasted way to add an admin panel to cakephp is to use a plugin: https://github.com/Maldicore/Admin
BrowniePHP could be helpful. Its a plugin for CakePHP that will save you time on backend development work.
This is very detailed and a great article on how to create an admin panel in cakephp - Cakephp 3 admin panel-Cakephp admin backend