We check this website, now cra-arc.gc.ca is up and dont blocked for our system and other users of the Internet.
So, answer to question: Is cra-arc Down Right Now? - NO! cra-arc is up!
If you have problem with access to site cra-arc, and domain cra-arc.gc.ca is not avalible.
Clear browser cache and/or try other web browser
(Chrome, Firefox or Safari).