MOSFET Selection criteria considering conduction losses, switching losses and working frequency
Since you have a resonant converter, you should focus more on the Rdson. The output capacitance also plays a role, during the dead time the output capacitance needs to be discharged. Be aware that the equivalent capacitance is the transformer, output caps of the FETs? as well as the reflected capacitance of the bridge rectifier
So, basically during the dead time you can consider the current through the inductance as constant.
This is the current that needs to discharge the equivalent capacitances.
If the output capacitances are large and dominant, then ic=c*dv/dt tells us that for a given C either the current needs to be large(large magnetizing current) or the  dead time needs to be large.
So yes, you want to have both a low Rdson and Output capacitance for resonant topologies, but in my experience the Rdson is far important.
Btw: are you sure about the secondary series cap?
This is only required for wireless power transfer. The presence of that cap makes the control complex.