Define and deploy infrastructure with an AWS CloudFormation template is the correct choice because it implements Infrastructure as Code so you can model and deploy identical stacks across Regions and accounts with automation and consistency.

Define and deploy infrastructure with an AWS CloudFormation template uses declarative templates to describe resources and their relationships. You can keep templates in version control and deploy consistent stacks repeatedly so results are reproducible and automated. You can use CloudFormation StackSets to push the same template across multiple accounts and Regions in a controlled manner which meets the startup requirement for speed and consistent results.

Use AWS Systems Manager Automation to create AMIs and apply patches is focused on operational tasks such as image creation and patching. It does not provide the primary declarative Infrastructure as Code model needed to define and provision full environments across Regions.

AWS Elastic Beanstalk streamlines deploying and managing applications but it is not a general purpose IaC tool for consistently creating diverse infrastructure components across multiple Regions.

Set up a CI/CD pipeline using AWS CodeStar helps orchestrate development workflows and code delivery but it is not the main service for defining and provisioning cross Region infrastructure templates.

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