There are two separate cases here.

Jean Monnet and Winston Churchill had a close relationship to the US. In their case, there is no exaggeration in saying that they were "deeply influenced".

Jean Monnet was the person who coordinated the joint allied maritime logistic traffic in world war I (a post himself suggested). In WWII he persuaded Roosevelt to develop the idustrial warfare effort and later served as coordinator.

Winston Churchill was the son of an rich american heiress and an aristocrat. As First (Comissioner) Lord of the Admiralty (1911-17), he recognize that: 1 - the navy should change of propellant, from coal to oil; 2 - the next war would take place in europe, against Germany, and conseguently a) started to displace forces to England, back from the Empire, (and possibly suggesting a greater role to the US), b) defended a bigger military collaboration with France.

These two men actually fit in the same description: -extremely pragmatic

• open to new ideias
  
• their actions are always triggered by the anticipation of the emergence of a greater power (first Germany, then Germany, later Russia)
  
• their solution is the same: join efforts, first with  the neighbouring great power(s) of similar size faced with the same greater menace (first france &england, then france&england, then france&germany, then with the indispensable distant and more powerful ally (the us).

As for Victor Hugo and Stefan Zweig, i cannot say without exaggerating that there is an influence on their ideias, namely political ideias, from american sources.
However, strictly in terms of political solution for Europe, i dare say that the US experience is marking, for a simple but strong reason: most of us, most of the time, are not capable of doing creative thinking on but a small number of concepts. And when we do, we generally enginner it by picking up concepts and applying them elsewhere, or by misunderstanding something in a way which accidentally simplifies the problem (still you need the ability of recognition). Even great minds like those resort to empyricism.
In the particular field of politics, this is captured by the following quotation - "the world respects only success" - which I saw attributed to Adolf Hitler, but i failed to track the reference (not even on-line).

I am not sure if Victor Hugo imagined a "United States of Europe" while he was far from his world, in the channel islands but let us examine his speech. Victor Hugo said In 1849, at the International Peace Conference,  from Wikipedia:

 "A day will come when we shall see... the United States of America and the United States of Europe face to face, reaching out for each other across the seas."

This is quite telling. Since we are at it, let us see a n entire paragraph. it is quite funny.

Italian writer and politician Giuseppe Mazzini called for the creation of a federation of European republics in 1843. This set the stage for perhaps, the best known early proposal for peaceful unification, through cooperation and equality of membership, made by the pacifist Victor Hugo in 1847. Hugo used the term 'United States of Europe' (États-Unis d'Europe) during a speech at the International Peace Congress, organised by Mazzini, held in Paris in 1849. Hugo favoured the creation of "a supreme, sovereign senate, which will be to Europe what parliament is to England" and said "A day will come when all nations on our continent will form a European brotherhood... A day will come when we shall see... the United States of America and the United States of Europe face to face, reaching out for each other across the seas." However, he was laughed out of the hall, yet returned to his idea again in 1851. Victor Hugo planted a tree in the grounds of his residence on the Island of Guernsey he was noted in saying that when this tree matured the United States of Europe would have come into being. This tree to this day is still growing happily in the gardens of Maison de Hauteville, St. Peter Port, Guernsey, Victor Hugo's residence during his exile from France.

* memo to ETelligence officers: dispatch an agent to take the a picture of the tree. *

so it was before he went to self-imposed exile. Hmm, that so before its political change of mind and the self-imposed exile folowing reactionary counter-revolution in France. So he initially defended  the U.S.E. as a prevention against the (intra-european) wars he had witnessed in his childhood.

Stefan Zweig eventually became also an exiled person, running away from the war - World War II. However, its belief in an federal Europe may have come earlier. It must have come as a solution to war. Which was a long concern from him. In its posthumous book "The world of yesterday. Memoirs from a European" he reported his meeting Bertha von Suttner, the (increasingly popular) person who persuaded Alfred Nobel to create his the Peace Prize.