In his Four Freedoms speech of 1941, how does President Franklin D. Roosevelt characterize World War II and the threat posed by fascism and Nazi Germany? Had he been alive at the time, do you think Roosevelt would have characterized the Cold War and the Soviet Union in the same way?

The Four Freedoms speech was Franklin D. Roosevelt's State of the Union address in 1941, at which time the United States had not yet entered World War II. In his speech, Roosevelt immediately turns to what he calls the "unpredecented" emergency of world events, by which he means World War II.
Roosevelt characterizes Nazism and fascism as a threat to the United States' democratic way of life and everything decent that way of life stands for. He mentions the "treachery" of the enemy—that is, Nazi Germany—in attacking and taking over Norway, implying that such tactics could be used against the United States. He argues that any policy of appeasement toward the dictators of the fascist world is doomed to failure and will not be used. He employs the negative term "dictators" to refer to the leaders of enemy countries. However, he does not specifically name these countries or their leaders.
As for World War II, Roosevelt does his best to get the nation ready for total war against the fascist regimes, saying that they could strike at any time without a declaration of war. He characterizes the war struggle as one of "defense of freedom." He says that the country must use all its resources, in addition to borrowing money, to equip both itself and other countries with the weaponry needed for defense against a ruthless enemy.
Roosevelt also links the United States' desire to spread the good life to all its citizens with the preservation of democracy and freedom. He calls for expanding social programs as a way to fight the enemy forces of evil in the world. He lists the four freedoms as follows:

The first is freedom of speech and expression—everywhere in the world.
The second is freedom of every person to worship God in his own way—everywhere in the world.
The third is freedom from want—which, translated into world terms, means economic understandings which will secure to every nation a healthy peacetime life for its inhabitants—everywhere in the world.
The fourth is freedom from fear—which, translated into world terms, means a world-wide reduction of armaments to such a point and in such a thorough fashion that no nation will be in a position to commit an act of physical aggression against any neighbor—anywhere in the world.

Although he does not say this, Roosevelt implies that since these are four freedoms that set us apart, they are what the fascists and Nazis do not offer to their people. These freedoms, he implies, are what the American people would lose should the fascists and Nazis win the war.
I think Roosevelt would have characterized the Soviets and the Cold War the same way, as the Soviet Union was also a dictatorship that denied average people freedom.