California Doubling. Somewhat ironically, nearly all scenes taking place in America were filmed in Sweden.
Dawson Casting: At the beginning of The Emigrants, Karl-Oskar and Kristina are in their late teens; Max von Sydow was in his forties, while Liv Ullmann was in her thirties. The characters' ages catch up with the actors' ages just before the end of The New Land.
Fake Nationality: Liv Ullmann is Norwegian, and was very worried that the Swedish audience would disapprove of her being cast as Kristina, as the character is essentially an embodiment of what it means to be Swedish. Turns out the audience liked her in the role.
Playing Against Type: In a film known and anticipated for its quiet serious drama, it made heavy use of inexperienced actors or actors mostly known for comedies.
Hasse Alfredsson, one of Sweden's most beloved comedians, played Jonas Petter. While Jonas Petter delivers some comic relief from time to time, for the most part it is a dramatic role far from the comedy Alfredsson is normally associated with.
Monica Zetterlund was mostly known as a jazz singer, had little acting credentials, and those in comedies, when she was cast as Ulrika.
For Helen Sjöholm as Kristina - she's had a long and successful career in Sweden as one of the country's most beloved singers and musical actresses, and is also so iconic in the role of Kristina that she was the only original cast member to appear in the English language concert version.
Peter Jöback, who played Robert. He wasn't entirely unknown before, having among other things voiced the titular character in the Swedish dub of Disney's Aladdin, but the role of Robert, and the massive hit song "Gold Can Turn To Sand", turned him into a superstar in his native Sweden, and launched a successful career as a musical actor abroad. He's appeared as Chris in Miss Saigon (winning the role after auditioning with the aforementioned song in Swedish), originated the role of Michael in The Witches of Eastwick, and has played the titular The Phantom of the Opera in London, New York and Sweden (being asked by Andrew Lloyd Webber himself to play the role - not to mention being Lloyd Webber's personal choice to play the Phantom when the show celebrated 30 years on Broadway).