Does it have to be production and not a staging environment? If that is the case, we do have a production demo account for sales reps in our app. We entered highly curated nearly 1-1 fake test to real-life data. So no hard-coded data or test-mode. It's very important that is feels 100% accurate from an experience standpoint. We created test users with emails we had access to, so they could still get emails from the platform as a demo user.
A customer of mine is using a demo server to demonstrate the service to customers. It's a service about money so using the production system with fake data would be difficult, especially for the interfaces with external services. The demo server is seeded with fake data. Google for faker and the language you're using and you'll likely find a good generator library.