Does the US2 sonar work with a 997. Does the switchfire sonar work with US2. Debating using the side image transducer unless you have too.

Yes the 997 will use the US2 if you only want the unit to be a 2D unit (set the transducer selection to Dual Beam).
Imaging has to come from the HDSI transducer.
If you want SI on the trolling motor you have to use the HDSI tranducer that includes the 2D Switchfire.

It will operate the Switchfire 2D Traditional Sonar but will not get you SI or DI readings that has to come from the SI Transducer.

I knew I wouldnt get SI but I had it on my last boat and kinda like the no wire down the trolling motor, and I upgraded to a 1197 on the console so my 997 has to go somewhere. But I like the bigger screen than the 788 the zx225 comes with. decisions, decisions.