These are main characters that had never had a lookalike in either their own time period or a different time period. I do not count a ghost of a character or a character pretending to be someone else (Cassandra, Olivia Corey, etc) as a lookalike. I also don’t count anyone appearing in one episode or Parallel Time.
1795:
Barnabas Collins, Sarah Collins, Angelique, Bathia Mapes, Suki Forbes, Judge, Riggs
1840:
Samantha Collins, Randall Drew, Roxanne Drew, Jeremy Grimes, Daphne Harridge, Gerard Stiles, Judah Zachary, Joanna Mills, Judge
1897:
King Johnny Romano, Amanda Harris, Julianka, Istvin, Garth Blackwood
Present:
Victoria Winters, Bill Malloy, Sheriff Carter, Dr. Woodard, Dr. Guthrie, Richard Garner, Frank Garner, Sheriff Patterson, Adam, Janet Findlay, Phillip Todd, Schyuler Rumson, Sheriff Davenport
Is there some I missed?