Customer is looking for a 2:1 I2C switch with level translation solution, and seems ADG3257 can be suitable for them. But I have a question regarding the HW configurations. Customer needs two I2C inputs with one I2C output, and the voltage level at input is +5V and output is +3.3V. In datasheet page-10 it shows one side can be +5V but I am not quite sure the +5V is at input side or output side?
The maximum data rate of the ADG3257 is 466MHz. This would be suitable for your application.