The plugin is freely available in Adobe Exchange and compatible with Photoshop CC 2018 and CC 2019: https://www.adobeexchange.com/creativecloud.details.102730.html.
You can also get it from within Photoshop by clicking on Window in the menu bar and selecting Find Extensions on Exchange...
On the Adobe Exchange website, make sure that the Extensions tab is active and simply search for "canto connector".
Once the extension is installed you might have to restart Photoshop.
Go to Window > Extensions and activate Canto Connect.
Select the relevant Canto Environment from the dropdown list. For US customers, it's usually "canto.com" while the rest of the world usually has "canto.global".
Log in using the same Canto credentials you are using when logging in to Canto in your web browser.
Allow the plugin access to your Canto account.
How to use the plugin
Note: The Canto Connector extension will not be visible on the Photoshop Dashboard, you need to create a new or open an existing file first.
Once a document is opened in Photoshop, your Canto Main Library is displayed within the extension, making it easy to work with images in Photoshop.
If you are looking for a specific image, simply enter your search term(s) into the search bar.
Alternatively, you can browse through your folders and albums.
Hovering over an image shows additional details.
While hovering and clicking on the little menu icon on the right, opens the detail view of an image from where you can open it in Photoshop or add it as a new layer.
The default behavior when clicking on an image can be changed under Configuration (2).
Furthermore, you can adjust the preview size to your liking (1) and filter what asset types you want to display within the Canto Connector extension (3).
All images you are currently working on in Photoshop are displayed under Assets. From there, you can upload them to Canto.
If the file already exists in your Canto account, you can choose how to handle the duplicate. You can either create a New Version...
... or save it as a New Asset in another album.