The meeting between Lenin and Stalin had much more with positioning the Bolsheviks within Russian radical politics than any systematic attempt to resolve the nationalities problem. This was part of a wider trend of Marxist parties in the twentieth century as they realized that the national issue was not being subsumed by growing class consciousness as Marx had predicted. Thus many of these parties sought to adopt Marxism around national ideas.
The previous year, members of the Socialist Revolutionary Party had endorsed an Austromarxist solution to the the nationalities issue. Formulated by Otto Bauer and Karl Renner, Austromarxism upholds the principle of national personal autonomy, a rather nebulous term that basically means that an individual has a right to declare their own nationality and would join in a federation of their respective national Marxist party. In August 1912, Austromarxism had received a significant boost when the Menshevik wing of the Social Democrats (SD) meet with the Bundists (a Jewish socialist labor group) and endorsed an Austromarxist solution for the Russian empire after the eventual revolution. Lenin, as a leader of the Bolshevik SD faction, saw it was essential to combat Austromarxism and differentiate the Bolsheviks from the larger movement. Lenin tasked Stalin to come up with an official position on the nationalities issue; one that would be congruent with Marx, serve the needs of revolution, and condemn the Bolsheviks' ideological rivals. Stalin's Georgian background added a non-Russian luster to this position paper. Lenin wrote to Gorky "we have a marvelous Georgian who is busy working on a long article 'illuminating' the proletarian solution to the national problem."
The resulting paper was the famous Marxism and the National Question attacked the principles of national personal autonomy and Austromarxism as a deviation away from Marx. The fundamental difference between the Bauer/Renner paradigm and Stalin's was that Stalin strongly asserted that a nation needs a territorial basis and must reside within a given territory. Austromarxism was thus a retrograde step according to Stalin as it diffused the strength of a Marxist political movement and would hamper the ultimate goal of Marxism after a revolution: the creation of a new socialist consciousness based upon class, not bourgeois concepts like nation.
The rub for all this is that the Bolsheviks seldom had nay clear and coherent policy with regards to the national question, much of it was ad hoc and conditional. Stalin would at various points between 1913 and 1917 assert an quasi-Austromarxist solution and Lenin was really ambivalent about Marxism and the National Question's paeans to national culture as too bourgeois. This ambivalence imparted to the Bolsheviks a degree of ideological flexibility and that made up for their lack of coherency during the Revolution and Civil War. Thus the Bolsheviks were able to harshly clamp down on the Ukrainian Rada's attempt to form an independent revolutionary Ukraine in the name of revolutionary unity while at the same time proclaiming to the peoples of Central Asia that the Bolsheviks were ending the tsarist "prison of the peoples."
The evolving Bolshevik position on Poles needs to be seen within this context. The Poles were a distinct ethnic and linguistic group according to the precepts of Marxism and the National Question. However, the Bolsheviks had a very flexible definition of exactly where this Polish territory actually lay. Thus Poles within the early USSR were in a dangerously anomalous position. The Bolsheviks would have seen ethnic Poles who refused to assimilate to the new ethnic republics (largely Ukraine and Belarus) were potentially agents or dupes of the Polish anticommunist state. The flexibility with regards to the geographic boundaries of Poland helps explains Stalin's Polish policies during the Second World War. He would justify the western shift of Poland as just correcting Poland to its natural historic boundaries and population transfers (aka ethnic cleansing) as an extreme, but logical, application of Marxism and the National Question.
Sources
Carrère d'Encausse, Hélène. The Great Challenge: Nationalities and the Bolshevik state, 1917-1930. New York: Holmes & Meier, 1992.
Martin, Terry. The Affirmative Action Empire: Nations and Nationalism in the Soviet Union, 1923-1939. Ithaca: Cornell University Press, 2001.
Smith, Jeremy. The Bolsheviks and the National Question, 1917-23. New York: St. Martin's Press, 1999.