Did any countries advocate for its independence? Or was it largely forgotten until the end of WWI?
There was public support for the Poles in the United Kingdom, but this did not translate into government action even during Polish rebellions, generally because the consequence would have been war.
See Palmerston's speech in 1848, defending the lack of support in 1831 during the Polish uprising.
I need not remind the House how deep a sympathy the sufferings of Poland excited in this country. Many things have passed in Poland since that time which the British Government greatly regrets, and in respect to which the rights laid down by treaty have been violated. But when we are asked why the British Government have not enforced treaty rights in every case, my answer is, that the only method of enforcing them would have been by methods of hostility; and that I do not think those questions were questions of sufficient magnitude in their bearing on the interests of England, to justify any Government in calling on the people of this country to encounter the burdens and hazards of war for the purpose of maintaining those opinions.
(If wikisource is not considered good enough, this collection has the same speech is a less convenient format.
The political and military inability of France, particularly evident at the time of partition of Poland (1772, 1793, 1795) make any forms of support impossible.
Poland in the nineteenth century occupies a discreet place in French historiography . The " Polish question " was exploited by the great powers and neither Napoleon nor Napoleon III do not want or can not really confirm their words with actions for the reconstruction of Poland. The question of the creation of the Duchy of Warsaw in 1807 , is generally addressed in terms of the Napoleonic policy. In this context, the recent historiography shows that there is far between reality and the image that we got , on Napoleon , a friend of the Polish cause. We can consider that in the Napoleonic period, the Duchy of Warsaw was especially a radiation and a strategic interests of the Empire .
Also because the Punishment of Polish insurrections in the 19th century and the emigration that follows , the links between French and Polish develop. However, the French historiography on this topic is quite old .
During the First World War, the Polish question was covered by the Franco-Russian alliance. One might think that the France of the Third Republic in this period will leads a bold policy of nationalistic support. That was not the case before 1917. Political and military relations between the French and the Poles in the latter part of World War I were low. In 1918, Paris was determined to promote the Wielkopolska as conceived by the Polish National Committee of Poland but instead they headed Jozef Pilsudski , who advocated a federal structure including Lithuania and Ukraine.
Sources:
Napoleon and Polish identity; History Today, Vol. 48, May 1998
Adam Halamski; Polish–French Relations, Yearbook of Polish Foreign Policy