To make the salmon filling, combine the salmon, mayonnaise, cream cheese, dill, horseradish, eggs, and pepper in a medium bowl and stir to combine well.
To make the shrimp filling, combine the shrimp, dill, mayonnaise, cream cheese, and pepper in a medium bowl and stir to combine well.
To assemble the Smörgåstårta, start by buttering the bread slices, either on one or both sides. Lay 1 ½ bread slices on a cutting board to form a long rectangle.
Top with half of the salmon filling.
Layer another 1 ½ bread slices on top, and top with half the shrimp filling.
Repeat with the remaining bread and fillings, ending with a layer of bread. You will have half a slice of bread left over.
Press gently on the sandwich from the top and sides to compress the layers a bit.
To frost the smörgåstårta, spread the top and sides with cream cheese.
Decorate with the vegetables and parsley (or other ingredients of your choice), any way you like.