“submerged floating”
Oxymoron..................
suspended in liquid?
Floating does NOT require an object be on the surface.
A vessel can float at varying depths. Think submarines: Their buoyancy is reduced to a point where they still float, but are below the surface of the water.
That’s all this tunnel is: a submarine with its ends on shore, tethered in place.
I hope this works, because that would be a great example in how to connect Vancouver Island to the mainland. A “tunnel” from say downtown Victoria to Port Angeles. It’s only 20-ish miles.