Web link competition between international sites

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I would appreciate some advice about how to handle an area of conflict
between different web sites.

One of my priorities at the moment is to increase the number and
quality of web links to our international web site, actinic.com. This
is primarily a doorway to our regional sites, including actinic.us,
which is maintained by our US distributor (we are a UK company). At
the moment our US links in particular are diluted, because some point
to pages on the actinic.com site and some to actinic.us. I want all of
them to point to actinic.com - but some of them need to direct
visitors to specific pages on actinic.us. I can think of several
possible ways of achieving this:

1) Create a host us.actinic.com that redirects either visibly or
invisibly through the DNS to .us
2) Use a bounce page (I don't like this idea!)
3) Use a 301 redirect
4) Merge the two sites and have .us and .com both pointing to the same
place. But this would create two domains with identical content.
5) Merge the two sites and have .us pointing to .com, but not the home

I would appreciate any advice on whether centralising our links is a
wise strategy overall, and which approach would be best from a SEO
point of view.

Thanks in advance.

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