the squealing can be both sensor and pads. If you hear it while moving slowly without applying brake then definitely sensor, but can also happen when applying brake. For the sensor potentially purchasing higher end sensor from quality manufacturer... I think i've heard of peeps grinding them down a little, but not sure on this. OR just remove them from the caliber and zip tie them to the abs sensor, so you don't get a warning.
The pads do squeal also. reversing and stopping does seem to cure this for a bit, but it comes back. Cool carbon pads have a great rep here... but they are rediculously expensive... i'm sure there's other brands that will work well. AND goo up the pads with brake quiet when installing them... the dealer doesn't do this. it can be vibration and/or brake dust.