Ahh... this I am on the same page with you.
Threats/Obstacles:
PCC and other NAN allies (eg Sioux)
Tir
Hestiby and her territory
San Fran
Amazonia
Horizon
Other Megacorps, particular Jap Corps (Renraku is now based out of LA? for their NA operations, or New York? I remember something about this in the Shutdown book).
CAS
Ghost Walker
Other Dragons including Sirrug
Draco Foundation
Ongoing civil war in Yucatan.
The military assault is not likely, not with the odds against them, but hey, you never know.
Divide and Conquer and Only Fight One War on One Front. Two important rules.
So first step is to resolve Amazonia Conflict. Make Peace or Win the War. This removes a massive thorn from their side. Step Two would be to resolve the Yucatan Conflict, same deal. Can't give away territory you don't control.
Step Three, sow confusion and discontent among your enemies. This is a shadow war. Distabilise CAS, PCC, and anyone else who might possible get in your way. Assassination, fund home grown terrorists (even if they would normally also hate you, eg Afghanstan during Soviet occupation, actually most major cold war events). Make sure its through double blinds and linked to you. The key here is to keep your enemies occupied and distracted and unable to act when you make your move.
Step Four, Take the Higher Ground. Before any actual terrirtory is taken, you must take the higher ground, at least in the public eyes. Massive media campaign painting you as the good guys and potential targets as terrorists, failed states, aggressors. eg Iraq, Poland, East Timor, WWI etc. Be attacked, defend yourself, play the victim guard, demand justice! or Big Brother, Human Rights card, eg failed state invasions. If Step Three is successful, it should provide justification.
Step Five. Attack! Just Don't Announce It! This step involves actually making your move, but always do unannounced. So everyone can see what your about to do, eg Step Four got you support, just don't set dates. Only the US does this and it could cost lives if you can't dominate your enemy immediately. See if you can be invited into the territory, perhaps by someone involved in Step 3 (rebel/freedom fighting groups), or can some sort of international body sign-off.
A lot of these steps overlap. Step 3 is where you would find the most work for shadowrunners, but there is lots of work in Step Four and Five. Runners could easily be involved in both the Azzies and Enemies side of the conflict. Step Four could be skipped in a more fiction, cinematic setting, and replaced with the 'Surprise Armada' scenario. You know, when the runners accidently stumble on a massive fleet/army just moments before the invasion.