This blog post explains the difference between these different apps. 

Different Types of Apps

1. Canvas App is a low-code platform for building rich business applications.
2. Model-driven app design is an approach that focuses on adding components such as forms, views, charts, and dashboards to tables using an app designer tool.
3. Power Pages is low code / Pro Code software as a service (SaaS) platform for creating, hosting, and administering modern external-facing business websites. We can say an advanced version of Power Portal (Previous Version)

Difference between Canvas App vs Model-Driven App vs Power Pages (learntoilluminate.com)

USE CASE
We have a Dataverse and Model-Driven App that is Managing Cub-Cake Orders. This MDA manages new orders and customer information. There is a third-party system that is handling the shipping process and updates the shipping information into a SharePoint list. We need the customer service department to be able to check the orders' shipping status and confirm shipment once complete.

Watch the Tutorial Part 1

Watch the Tutorial Part 2