Nowadays, QA required and responsible for coordination in Release Management for own accountability of quality and timeliness of project delivery. How do you even get started to test for a Web Site that has been migrated? Of course, QA wants to have strong Web Strategy and Testing Team in place. Probably another useful step is to just get a feel for the overall scope or checklist of a migration, before diving into any particular details (or just starting without planning). Perhaps this one page checklist will help your planning by providing some ideas of the scope of migration planning for testers.
Navigation - Link Verification.
Randomly browse the site (internal links) to look for any wrong behavior.
Form submissions & page redirections.
Links/references in emails / messages.
File uploads - permissions & paths verification.
An email, site URL details correctly set in configuration.
Write permissions on all uploaded directories.
Functional verification affected due to migration.
Data cleansing .