Which additional step should the solutions architect take?

Explanations:

While migrating to Amazon RDS for MySQL with a cross-Region read replica in us-west-2 can provide some level of data redundancy and can help with failover, it does not meet the required RTO of less than 5 minutes and RPO of less than 1 minute effectively. The replication lag can be higher than 1 minute depending on network conditions and load.

Migrating to an Amazon Aurora global database with the primary in us-east-1 and the secondary in us-west-2 is the best option. It supports cross-Region replication with an RPO of less than 1 minute and can provide fast failover capabilities, making it suitable for achieving the required RTO of less than 5 minutes.

An Amazon RDS for MySQL instance with a Multi-AZ deployment provides high availability and automatic failover within the same region but does not support cross-Region failover, which is necessary for the setup described. Therefore, it cannot meet the requirement of a cross-Region disaster recovery solution.

Creating a MySQL standby database on an EC2 instance in us-west-2 may provide a manual backup solution, but it would not ensure automatic failover and could lead to an RPO exceeding 1 minute, as it would depend on the frequency of data synchronization between the primary and standby databases.