Hi,
The canonical URL needs to be a valid URL of the product. You can't put a random URL in there.
So it's better to leave it empty if you don't know what you put.
I don't see why the description wouldn't be displayed based on the URL. It must be something, like a problem with your template.
Try to switch temporarily to the default template of Joomla and see if the product page displays normally. If so, then you should contact your template provider as there is apparently a problem with the view override of the product page in the template.