Hi @HSheild ,
Do you want to copy your Environment to a Sandbox Environment?
Which option do you choose when you copy a Environment? Everything or Customizations and schemas only?
Further, is the canvas app from your Source Environment has been added into a Solution already?
Currently, there are some known limits with the "Copy" Environment functionality in Power Platform Admin Center. Currently, any components that have not been added to a solution (including canvas apps, flows, custom connectors, and connections) will not be copied to the target environment.
On your side, please make sure the canvas app from your Source Environment has been added into a Solution already in your Source Environment.
Please check the following article for more details:
https://docs.microsoft.com/en-us/power-platform/admin/copy-environment
In addition, if you the canvas app from your Source Environment has been copied to your Target Environment successfully, you need also to modify the Case form in your Model-Driven app, to make sure the embedded canvas app references the canvas app in your Target Environment rather than Source Environment.
Best regards,