If you have no mirror heat switch on either the door ? or dash mirror controls then maybe no heated mirrors. Somewhere in the cargo or spare tire area there's a "service parts ID" sticker - the RPO (Regular Production Option) codes for what's built into THAT vehicle. Find it and decipher the codes using a correct model year Google search for " XXXX cadillac gm rpo code definitions".

Heated mirrors are further discussed in the owner's manual .............

Typical RPO sticker -

 

Yes a wealth of information to be found in the owner's manual!

However I think this may be standard on all vehicles, because anything optional in the owner's manual always starts with "If the vehicle".

 

Drivers side mirror is heated on all but the base model. Premium and Performance have both sides heated. They operate when the rear defogger switch is used.

 

I think some also have a dimmer that has wiring to it as well.

 

Pull the mirror off. It’s easy. If there are wires connected to it, it’s heated.

 

In general, if you have a heated rear window defogger, you have heated mirrors. Both sides. There is no separate switch.

I am pretty sure all SRX of this generation have power mirrors on both sides which means they all have wires.