Debates over whether or not the idea of a "Schlieffen plan" actually existing aside, the Plan itself was kept fairly secret, with wargaming of scenarios based on it being few in number, and knowledge of the actual plan being restricted to high ranking war ministry and General Staff members.
That being said, to an extent the French and the Russians had guessed German intentions before. The French formulated Plan XVII with the expectation that the Germans would invade through southern Belgium (ie south of the Meuse) and Luxembourg, avoiding the bulk of the country while also avoiding most of the French fortress line. Hence Plan XVII envisioned placing two French armies inside Alsace-Lorraine via offensives to threaten the German advance from the south, while three armies to the north parried and reversed the main German attack. Likewise, the Russians promised to mobilize '800 000 men' to be sent against presumably weak German opposition, in support of the French, while two thirds of Russia's mobilized forces would move against Austria-Hungary.
When the German invasion actually came, it was certainly a surprise for France, Britain and Belgium. The French did not expect an invasion of Belgium on such a wide front, and with all of Germany's reserve divisions committed. The British were shocked considering that the invasion encompassed the whole country; had the invasion taken place as the French believed it would, the chances of British involvement would have been greatly reduced. Few were also prepared for the ferocity of the German attack: in spite of Belgian civilians having been told to avoid altercations and largely heeding this advice from their government, the invading Germans lashed out at 'francs-tireurs' real or largely imagined, and c. 5600 Belgian and c. 900 French civilians were murdered, and tens of thousands of homes destroyed. Dinant and Lueven (including it's university library) were almost completely raised.