The history of Napoleon Bonaparte actually stated that Napoleon favored Tsar Alexander I in his campaigns and did not wish to invade Russia. The negotiations and meetings he held with Alexander I brought about the agreement that Napoleon would not attack Russia, as long as Russia ceased trade with Great Britain instantly. Alexander I agreed at first, but secretly traded with Britain as Russia's poor economy badly needed a boost. Napoleon soon found out and was really angry, thus leading to the invasion of Russia.
If Napoleon hadn't invaded Russia, and instead focused his Grande Armee powers on the invasion of Spain, things would've turned out quite differently. The Russians exploited the Grande Armee's weaknesses by burning the ground so as to prevent the French from obtaining food sources naturally, and also delaying the French advance so that they can suffer from the Russian winter. Moreover, Napoleon made a fatal flaw in his Russian campaigns by directly assaulting Moscow, without knowing that Russia's administration system was actually comprised of smaller governmental bodies that were stationed in various cities and districts scattered all over the nation. As a result, his conquer of Moscow did not harm the armies of Russia much, except to hamper its morale by a little.
The Haiti Revolution caused Napoleon to immediately detach large portions of his army to repel the Haitian rebellion. If the Haitians had not rebelled, Napoleon, of course could have focused his entire army bulk on the conquest of Europe.