Choosing transistor for this circuit
simulate this circuit &ndash; Schematic created using CircuitLab

The sensor will always be connected to ground on one end. The power supply can be enabled or disabled by the MCU. this is just the basic FET based switch. Advantage here is that, the sensor can always have ground reference. FETs can be from TI. the threshold voltage is well with in 2 V to turn on the FET.

Correct me if i am wrong.