As said by Kevin, all required facts are available in Lieven books, one of the best I read on Russian-French war. Sokolov "Le combat des deux Empires" is more than a complement to it.
To sum them up:
Having direct access to french order of battle, Alexandre knew that only small forces were present in Prussia and Poland.
A good part of his power rested on the support of high nobility, who considerably augmented their whealth by gigantic domains in eastern Poland (now Bielorussia / north-western Ukraina). The very existence of Great Duchy of Warsaw was a threat to these situation.
As all tsars since mid-17th century, Alexandre tried to shift polish allegiance towards Russia, proposing himself as king, under the system of "one sovereign, two kingdoms" that he already used in Finland, and that will be implemented in Poland from 1815 until the 1830 revolt.
He mobilized years before Napoleon, armies large enough to deal with all french forces. His plan was to be crowned king by the Poles, then to fight Napoleon with their help and those of the Prussians.
But polish reaction was totally negative, and Napoleon mobilized an army so huge that Alexandre discarded any invasion plan. At this step, Napoleon would not simply demobilize, having wasted millions in military preparation and leaving two large russian armies at the outpost of his empire.