Looking to shoot through a coral viewer about 6-10 inches below the surface. I honestly don’t get the camera lingo most of the time so looking for suggestions! Thank you.
Depends entirely on your budget. Canon has a new lines of lenses for the R-series mirrorless cameras and they are pricey.
See here for a good discussion of Canon macro lenses.
I purchased a used Canon 100mm 2.8L lens from eBay this weekend based on suggestions I found here on R2R. They can be found in good condition for around $500.