You can use whatever topology you like / you have experience with. If you have experience with class-D, just try it, as this is an easy to build topology at your power level, and you may only need to sweep frequency to find a good operating point. Do you have any idea of the impedance of the transducer as you need this to design the matching/filter circuit that is between the half (or full) bridge stage and the load?
Regarding other topologies: In the recent past high power ultrasonic converters (kW range) were built with extremely fast switching thyristors. LC resonance was used to turn-off the thyristor. For some years ago I wanted to use thyristors in a high power half bridge application, but very fast thyristors are obsolete, or at least hard-to-get. It became a resonant converter with fast IGBTs and SIC rectifiers.
If you can use supply voltage < 100V, I would go for a mosfet output stage because of ease of drive, good switching speed and low Rdson.