The "best" you can get is a Israel-Palestine esque situation where a few small territories are the constant focus of mostly indirect and sporadic direct warfare. This would require Germany and France to be both undefeated and relatively secure in both their economic strength and mutual hatred. Maybe something like the following:
Germany stalemates France and keeps its Brest-Litovsk gains. War ends 1919 with a lot of bitter feelings.
A generation or so later, Russia bereft of Ukraine and Belarus is either Soviet or fascist and demands a rematch with Germany, which in turn leads to a rematch with France. The main front is in Eastern Europe, with French help to Russia and French and German armies mostly just staring at each other angrily in the west. Germany loses this battle and is stripped of its eastern holdings and Alsace-Lorraine, where an active anti-French insurgency develops.
By about 1940-1950, Britain and the US have decided that the Franco-Russian entente is more than enough to check the Central Powers, so they cooperate with the latter to maintain the geopolitical balance. All sides probably have nukes by this point.
National and religious insurgencies supported by Central Powers active in Balkans, Franco-German border, and perhaps the Near East in opposition to the Franco-Russia entente. Germany and its central European clients are poor and illiberal enough that continuous low-level warfare is politically acceptable, and the more affluent Franco-Russians keep step. The Anglo-Americans are happy to trade with all.
Anti-war movements will crop up in both sides by the latter half of the 20th century, but given the strength and motivations of the two blocs involved, the war may continue for decades to come.