A 50mp FF from Canon will have much better IQ than the 7D II. Pixel size is immaterial, sensor size and sensitivity (Q.E.) is what matters. On a normalized basis, such a camera should crush the 7D II in terms of IQ, because your averaging together all those tiny pixels to produce the same output resolution. That's the same as having bigger pixels.
That would be for a b/w image; in color the downsampling gives you higher chroma information density and a reduction of sampling artefacts for free. I.E. the higher resolution camera gets an additional headstart.