BTW, this is all my personal opinion. I am not trying to offend anyone. These are just who I pictured while I was reading the books.
Chiron - Liam Neeson
Percy - Chris Evans
Jason - Chris Hemsworth
Annabeth - Emily VanCamp
Piper - Tessa Thompson
Nico - Tom Hiddleston
Will - Jeremy Renner
Reyna - Scarlett Johansson
Lavinia - Florence Pugh
Meg - Hailee Steinfeld
Frank - Sebastian Stan
Hazel - Elizabeth Olsen
Leo - Anthony Mackie
Thalia - Brie Larson
Calypso - Natalie Portman
Now for the gods......
Zeus - Sean Bean (already a great Zeus)
Hera - Liv Tyler
Poseidon - Viggo Mortensen
Dionysus - Stanley Tucci (already great)
Hermes - Pedro Pascal
Aphrodite - Miranda Otto
Hades - Johnny Depp
Apollo - Orlando Bloom
Artemis - Emma Watson
Athena - Hayley Atwell
Demeter - Also Natalie Portman
Hephaestus - Richard Armitage