How might the Soviet Union exploit an Anglo-American war?

Would the Soviet Union simply seize Europe during a 1946 Anglo-American war?

Not necessarily; Stalin would probably choose the alignment that best weakened the United States while preserving Soviet security in Europe.

The United States appears as Stalin's principal long-term capitalist threat, making Soviet strategy opportunistic rather than mechanically expansionist. Existing Soviet control in Eastern Europe reduced the need for an immediate westward conquest, while an alliance with Britain might isolate American forces and open pressure through the Far East and Alaska. The Soviet Union could not seize the rest of Europe without consequence because European alignment would determine whether American or British power opposed that move. Britain's Labour government also distrusted Stalin in part because Soviet claims to socialism damaged Labour's own political position. The scenario ultimately depends on why Britain and America went to war and which European states joined them.