AWS Redshift migration from an Amazon account in CA region to an Amazon account in US region

One the easiest approaches is to share a recent snapshot with the target account, and then restore the cluster in the target account/region. Please refer to the snapshot sharing documentation for the related steps.

To migrate an AWS Redshift database from a Canadian region to a US region across different Amazon accounts, you'll need to follow a few best practices and consider some key points:

1. Cross-Region Migration: Since you're moving data between regions, you'll need to use AWS Database Migration Service (DMS) to facilitate the transfer. DMS supports Redshift as both a source and target.

2. Cross-Account Setup: You'll need to set up the necessary IAM roles and permissions to allow DMS to access resources in both the source and target accounts.

3. Staging Area: DMS will use Amazon S3 as an intermediate staging area. Ensure you have sufficient S3 storage in the target region to accommodate your 3TB database.

4. Replication Instance: Create a DMS replication instance in the target US region. Choose an instance type that can handle your 3TB workload efficiently.

5. Network Configuration: Set up VPC peering or AWS Direct Connect between the regions if possible to optimize data transfer speeds.

6. Full Load followed by CDC: For a 3TB database, start with a full load migration, then use Change Data Capture (CDC) to sync any changes that occur during the migration process.

7. Parallel Load: Utilize DMS's parallel load capabilities to improve performance. Adjust the MaxFullLoadSubTasks parameter in your task settings.

8. Compression: Use compression for both the S3 staging area and the target Redshift cluster to optimize storage and transfer speeds.

9. Distribution and Sort Keys: Ensure your target Redshift cluster is configured with appropriate distribution and sort keys for optimal performance post-migration.

10. Validation: After migration, thoroughly validate the data integrity in the new Redshift cluster.

11. DNS/Application Changes: Update any applications or services that connect to the Redshift cluster to point to the new endpoint in the US region.

12. Performance Tuning: After migration, monitor and tune the performance of your new Redshift cluster in the US region, as query patterns may be different due to the region change.

Remember to test this process thoroughly in a non-production environment before attempting the actual migration. Also, consider the potential impact on data residency and compliance requirements when moving data from Canada to the US.
Sources
Using an Amazon Redshift database as a target for AWS Database Migration Service - AWS Database Migration Service
Amazon Redshift database as a target for AWS Database Migration Service (DMS) with best practices | AWS re:Post
Understand and optimize replication for Amazon Redshift with AWS DMS | AWS Database Blog