It would be very difficult to choose a BLdc motor without knowing your machine specs. You need to know
All leadscrew pitch
Machine weight for each axis. If you have a gantry cnc, how heavy is it. This is used to calculate your required acceleration.
Do you want pulley reduction or direct drive. If pulley reduction, what ratio.
The required maximum feedrate.
How much cutting force is required for each axis. Cutting metal usually requires more than wood.
Probably a few things I forgot to list but there really isn't some easy way to say that this servo motor is equivalent to that stepper. A servo motor of equivalent size to a stepper will have lower torque but run at much higher rpm. This usually requires some kind of gearhead or pulley reduction to utilize a servo motor to its fullest potential.