Saying they are on different sides implies they are still involved in this timeline; was that your intent? And obviously the outcome depends on who joins which side. It's hard to see either joining CP, but strange bedfellows, I suppose. If Britain decides to support CP (maybe the French/Russian alliance with France hostile to Britain leads to Russia squabbling more with Britain in Central Asia or something, so Britain jumps at the chance to fight Russia with the support of powerful allies), Belgium may just go along and also join CP (or at least let the Germans through without complaint), and France probably falls quickly, with Russia either seeing the writing on the wall and also giving up quickly or suffering even worse than OTL. Probably Italy never joins Entente (giving the Franco-Russian faction that name for convenience; it doesn't seem any less appropriate than continuing to call a faction that includes Britain the Central Powers, and I'm not going to bother to invent new names for this brief speculation), Ottomans and Bulgarians may join CP sooner. Really, with no British blockade and perhaps a BEF helping the Germans, hard to see how the war doesn't end very quickly, with probably a much more reasonable peace settlement as a result of the much shorter war (also helped somewhat by the fact that even a CP-friendly Britain wouldn't really want their CP allies making excessive gains). In the Far East, Japan presumably honors its alliance with Britain, and so may gain some Russian territory when the Russians submit.
If instead the scenario is that France is somehow convinced to join the CP, to give up their dreams of recovering Alsace-Lorraine in exchange for divvying up the British Empire, things again go ill for Russia. And if the CP can pressure Italy into joining the winning side, the Royal Navy will face a challenge trying to both keep the Germans bottled up in the North and maintain operations in the Mediterranean against very strong opposition. The strength of the Royal Navy could make the war of Britain essentially alone against the expanded CP a long slog, though, likely ultimately bankrupting Britain (as the real war nearly did) and as the CP probably eventually wins, likely a bitter peace settlement that involves Britain giving away a lot of its colonial possessions to the CP. It's an interesting question what happens to Japan on this scenario; do they stay loyal to their alliance with the British, and if they do, will the CP ever get around to trying to fight them or will they accept a status quo antebellum on that front to get the war over with? It does seem unlikely that they'd gain anything in any event.
But details matter a lot. Obviously, in either scenario, diplomats will not be idle; whichever country doesn't join CP in your scenario will be trying very hard to find other friends, and if they are successful enough that could of course substantially change either scenario. Certainly if the Entente can somehow get the U.S. to support them from the beginning, for example, that would do a lot to balance out the massive strengthening of the CP in these scenarios (not sure how they do that, but not sure how CP get either Britain or France to join either, as I said).