Two to look into are Ningaloo, Western Australia or the Socorros Islands in the Pacific from Mexico. Probably the Galapagos Islands also but I'm not sure about there.
Ningaloo is land-based, the Socorros are via liveaboard from the San Jose del Cabo area of Mexico. You will definitely dive with Mantas on a Socorros trip and certain times of the year Whalesharks pass thru there.
A couple boats to consider are the Solmar V, the Nautilus Belle Amie or the Rocio Del Mar. Since it's a special trip, Belle Amie is the newest/nicest of the 3.
I've seen more than one video of snorkelers following whalesharks off Ningaloo when some Manta's fly by - IDK if they allow diving with w/s's there - mainland Mexico or Utila - 2 known whaleshark destinations - don't - just snorkeling. Which is still great, we did that off Utila a few years ago.
Southern Belize is pretty reliable at certain times late spring/early summer for Whaleshark diving and the Manta Night dives off Kona are world famous for that. I've never heard of whalesharks in Hawaii though and I dove there multiple times.
Somehow the Donsol area of the Phillipines sticks in my head for both also seasonally. Some of the South Pacific locations like Yap are pretty reliable for Manta's IDK if they ever see Whalesharks though.
hope this helps narrow your search.