It's basically to show who can be ordered to do further tests and studies or label changes, for example. It's usually identifying a group of people who are the regulated parties. That's usually the drug companies or the warehouses that move the product and that hold an establishment licence.
The definition of “a person who sells” is much broader, and it could include a pharmacist. For recall, you really do want to reach through to everybody who's going to be distributing. Pharmacists aren't licensed by Health Canada to do what they do, so you do want to pick up the sale aspect.