The question asks for three recommended practices when migrating a J2EE application to the cloud, with the operations manager as the stakeholder. Based on the community discussion and best practices:

• C (Instrument the application with a monitoring tool like Stackdriver Debugger): Essential for monitoring and debugging the application post-migration, ensuring operational visibility and quick issue resolution. This aligns with the operations manager's focus on application stability and troubleshooting.
• D (Select an automation framework to reliably provision the cloud infrastructure): Critical for infrastructure automation, enabling consistent, repeatable deployments and reducing manual errors. This is a core cloud migration best practice, especially for operational efficiency.
• E (Deploy a continuous integration tool with automated testing in a staging environment): Supports continuous delivery, automated testing, and quality assurance, which are vital for maintaining application reliability during and after migration.

Other options are less suitable:

• A (Port the application to Google App Engine): While App Engine is a managed PaaS, porting is not mandatory; the application could run on other GCP services (e.g., GKE or VMs). It is service-specific and not a universal practice.
• B (Integrate Cloud Dataflow for real-time metrics): Overly specific and not directly related to general migration practices; real-time metrics are optional unless required by the use case.
• F (Migrate to a managed NoSQL database): Unnecessary without a stated need for NoSQL; the existing MySQL may suffice, and this could introduce unnecessary complexity.

The consensus from the discussion (e.g., CDE has 47% support and upvoted comments like apb98's) emphasizes C, D, and E as foundational for operational readiness, automation, and testing, without locking into a specific service like App Engine.