Merckx has won every monument, every grand tour and the WCRR placing him at 9/9. He's the only one to have done so. Nobody else even has 8/9 or podiums in 9/9.
With a podium in Roubaix however Pogacar could become the 2nd rider to get a podium in each.
Victories
9 - Eddy Merckx
8 - /
7 - Felice Gimondi, Bernard Hinault
6 - Tadej Pogacar, Rik Van Looy, Louison Bobet, Fausto Coppi
5 - Francesco Moser, Hennie Kuiper, Sean Kelly, Vincenzo Nibali, Roger De Vlaeminck, Philippe Gilbert
Podiums
9 - Eddy Merckx
8 - Felice Gimondi, Tadej Pogacar, Herman Vanspringel
7 - Bernard Hinault, Rik Van Looy, Louison Bobet, Francesco Moser, Hennie Kuiper, Sean Kelly, Gianni Bugno
6 - Fausto Coppi, Vincenzo Nibali, Roger De Vlaeminck, Philippe Gilbert, Moreno Argentin, Alejandro Valverde, Greg LeMond, Raymond Poulidor, Fiorenzo Magni, Joaquim Rodriguez
Top-10s
9 - Eddy Merckx, Felice Gimondi, Herman Vanspringel, Rik Van Looy, Francesco Moser, Raymond Impanis
8 - Tadej Pogacar, Bernard Hinault, Louison Bobet, Hennie Kuiper, Sean Kelly, Alejandro Valverde, Greg LeMond, Raymond Poulidor, Jacques Anquetil, Jan Janssen, Laurent Jalabert, Freddy Maertens