Hi,
The MC7455 is the main unit that Sierra would offer, the architecture is slightly different in that it uses QMI rather than the older CnS which is no longer supported on any devices. Depending on how you are using it, it may or may not be able to be easily integrated into your system, you would need to give a few more details. On the hardware side it is broadly compatible but you will need to look at the pin outs to compare to what you have on your board at the moment.
Regards
Matt