In the Microsoft Store there is a page for everything, including the full version with both modes. If the sum does not come out, that is because in the 43.01GB there is also a pack of skins included in the aforementioned total version, which weighs around 620MB.
Do not worry because, even if they are separate downloads, the campaign and multiplayer come in the same purchase, as already confirmed. Next April 3 will be when Resident Evil 3 Remake goes on sale.