Alien Registration number for UI application

What is a "major attachment claimant"?

I don't know, nor care.

Since you are not collecting Cdn EI (you would be eligible for state UI if you move to Canada, not Cdn EI), nor should you.

What you need to be familiar with is the UI regs in your state of employment, and how you're living in Canada entitles you to THAT UI (not Cdn EI).

The regs for Cdn EI don't apply to you.