I don't think the entirety of Pacific Front allied with China, only Japan.
Also, STILL nothing about the southern Pacific Front. They might just be their own subfaction now.
Japan wanted to, for sure, I will admit I'm not sure about the rest being in on this though (South Korea, for example; they were having a ceasefire with North Korea from the looks of it, so I kinda assumed South Korea was in on it too).
The main problem though is that it might as well be almost the entirety of the Pacific Front; looking at the maps where PF is based from (Skirmish screen; not the most reliable at times, but it's what we got), the major powers in the PF are Japan and Korea. Like you said, We've heard nothing about Australia's involvement within the Pacific Front. Nor do we know about any other members of the PF. The main members are Japan and Korea from what I saw, and one wanted to join China, and the other was sorta going along with it. So it may as well be the entirety of the PF wanting to be with China except for a few small groups and individuals like Kanegawa Industries and Norio. That's why I don't really feel too bad about PF losing their countries to China, getting beaten up, etc. Because 95% of the PF are traitors to the Allies, no questions about it.
Not exactly, he's just invited to the invasion. If you see Side Effect, the Soviet would also question why PF is attacking them when Chinese has set their feet there. The treaty between them had already begun far before Yuri gave the Chinese a Psychic Beacon. Some part of PF (like Norio and Kanegawa Industries) doesn't agree to this though
So PF and China were already planning to stab Soviet Russia in the back, even before Yuri started to make his own plans to undermine the Soviets (Russia, specifically). Not surprising; the countries involved (China, PF members Japan and South Korea) have a history of stabbing their allies in the back. In this mod, China did this to the Soviets, while the PF did this to the Allies. Go figure. XD
Like I told Solais, Norio is only one man compared to the overall PF military. One man cannot win a war, as they say (inb4 someone proves me wrong with in-game evidence. XD). Kanegawa Industries, while making some very strong contributions to the Allies (Cryocopter, helping to build the Paradox Engine), are only one weapon firm. They were reliant on the PF military to protect them while they did their work, and the PF military did a pretty sh*t job at that. China was all over Japan according to the campaign, and reading the Harbinger's and Future Tank Alpha's respective descriptions, it sounds like KI's research labs and factories were either shut down or taken over by the Chinese, with KI executives essentially giving up after realizing that the PF is doing a really sh*tty job defending their countries. Most of the PF wanted to go along with China, regardless of the misgivings of individuals like Norio and groups like KI. And they were punished like the traitors they were (See: Rewarded as a Traitor Deserves).