The Russian Axis and British-German Axis are the Great Powers and their respective colonies and protectorates that are definitely going to be involved in the war. Pro-Russia and Pro-British/German are countries that haven't officially allied yet and thus aren't guaranteed to enter the war, but have a pretty high chance of doing so. The Neutral Pro-Russia and Neutral Pro-British/German are countries that politically favor one side but will likely not enter the war. Grey countries are neutral countries that don't politically favor one side or I'm unsure where they fall under.
Cliff notes of notable countries:
Russian Axis
Russia and the Russosphere
Pro-Russia
Socialist Countries: France, Spain, Portugal, Italy
Denmark?
Revenge against Britain during Fashoda and reclaim Greenland/Iceland.
Continental/Revolutionary Mexico
Currently at war with Germany
Neutral Pro-Russia
United States and their sphere of influence (Hispaniola, Panama, Nicaragua, Honduras, and El Salvador)
While they politically favor Russia, the US will likely sell to both sides to boost their lagging economy if their current war with Mexico/Germany ends by the time Fashoda II starts.
Persia
While technically "neutral", Russia has the ears of the Shah and made more inroads compared to Britain
Switzerland
Rio Grande do Sul
The only member of the Russosphere that isn't likely to participate in the war since Russia doesn't have a strong enough influence to turn them into a protectorate.
Neutral
Japan (+ Taiwan)
Focusing internally on their political and economic instability and the Philippines. Not sure whether they currently favor one side.
Second French Empire (North Africa + Suez + Hainan)
Might be pulled in Russia's camp depending on how aggressive Britain is with getting back the canal. But currently listed as neutral since they don't like Russia interacting with mainland socialist France.
Afghanistan
Kingdom of Italy (Libya)
Other Latin American countries
Not too sure where they fall in...
Hawaii
Neutral Pro-British/German
Gran Colombia (Venezuela and Colombia)
Pro-British/German
Qing Dynasty (China)
Greece
Chile?
They also took out additional loans from Britain a couple of years back. But, they are still embroiled in the war...
British-German Axis
Britain and the Imperial Federation
German Empire