Huh, what would an MCU do? You still need an RF detector (no MCU ADC has a short enough aperture to directly sample RF), and you get isolation for free with a current transformer (which is needed anyway). Just wire it back to any receiver (scope, spec, wattmeter..) and watch in real time. It's not going to be anything different with power level, just test with some standard power level in each band, something like that, right?
If it's because it could be very remote e.g. up an antenna tower, and you don't want to run signal cables up to a sensor... I feel it would be much easier solving such problems mechanically in the first place: use a proper balanced antenna; use voltage baluns (or combinations of current and voltage baluns!), use grounding to the tower, use grounding where the feedlines reach ground, or again at the shack; put more current baluns inbetween ground points, etc. Don't forget to test and debug these at ground level: antennas and baluns can be tested, at least to whatever extent is feasible with respect to the size and height over ground (that is to say, given whatever response it should have in that environment), and baluns can be checked for balance with a simple jig, say precision resistors to GND, on a GND plane, and measure CM and DM with a LISN (current choke, one end grounded, other end shield tied to a CM RF port).
Testing and trimming won't perfectly cancel CM anyway, nor account for proximity say if the elements are long and may approach structures/trees (especially if the antenna is rotating). So there's only so much prep you can do, and the rest can be dealt with by choking and grounding.
Tim