As sherilaine mentioned, they do meet in Fantasyland. When enter FL from MS, veer to the left (the side with Snow White and Pinocchio). The building with Olaf on the roof will be visible. If you end up on the right side of FL (Peter Pan side), you might miss the building; I was surprised that it's actually on the harder side to see when approaching from Mr. Toad/Alice/Mad Tea Cups.
As others have said, prepare yourself for a long line. Most recent reports indicate that your best chance at seeing Anna and Elsa together are first thing in the morning (when the M&G opens).