Multi-domains: Redirect traffic from all domains to a given site?

Upon sign-up for Multisite, for multiple domains, is there a way to

(1) Automatically assign traffic from each domain to redirect to the selected domain?

(2) Without any set-up required by users?

For instance, with the Multi-Domains plugin I have greenboard.ca as root domain and greenboard.us as alternative, using multi-site sub-directories (i.e. greenboard.us/site1). If a user chooses greenboard.us/site1, I need all traffic from greenboard.ca/site1 to redirect to greenboard.us/site1, or visa versa if they choose greenboard.ca/site1.

The reason for this is I am using dynamic links, all of which contain greenboard.ca/{dynamic-sitename}, and will not work when using greenboard.us unless the .ca traffic redirects to .us. For example, this test site won't work: http://www.greenboard.us/test12 - Click on the photo to access the portfolio page, then click on My Advertisements to return. Instead of returning, visitors are redirected to greenboard.ca. This is because the link specifies greenboard.ca/test12, not greenboard.us/test12.

And I need this to be fully automatic, without any set-up by users.

Plus, on my wish list, is it possible to add a menu item "Select Domain" for sub-site users to be able to switch between domains (e.g. from .us to .ca to .eu to .co.uk etc)? Users who move from one country to another will want to be able to change the URL to match their new country.

Thanks,
Rob