How to deal with address issue when expanding to US market

I am currently selling on amazon.ca however I would like to expand into the US market but it seems like all my ungated categories in Canada are still gated in US and I need to do the ungating all over again.

1. How do i gate ungated when i am using a prep center?

2. Do I need to change the address in my US seller account to my prep centers address.

3. Does changing address in one area market affect another.

I have tried reaching to seller central customer services and no one was able to help.