As far as the Sardinia and Corsica garrisons go, English language sources on-line are mixed, but from what I can tell, in the summer of 1943, it stacked up as follows:
German: 90th PGD (Sardinia); SS RF PG Brigade (Corsica);
Italian: 20th Infantry (Corsica); 30th Infantry (Sardinia); 31st Infantry (Sardinia); 44th Infantry (Corsica); 47th Infantry (Sardinia); 184th Parachute (-) (Sardinia); 203rd CD (Sardinia); 204th CD (Sardinia); 205th CD (Sardinia); 225th CD (Corsica); 226th CD (Corsica);
That's a German motorized division, four Italian infantry divisions, and three Italian coastal divisions in Sardinia, and a German motorized brigade, two Italian infantry divisions, and two Italian coastal divisions in Corsica. Obviously, a German or Italian division was not directly comparable to a US Army or British Army division in 1943, but the Axis forces in Corsica were (roughly) equivalent to four reinforced Allied divisions and those in Corsica were (roughly) equivalent to two reinforced Allied divisions. So call it two corps equivalents between the two islands, both significantly smaller than Sicily, which would suggest an Allied expeditionary force that would have to be roughly an army in size - so about half to two-thirds of the HUSKY assault force?
That all appeared in the latter spring & summer. Most had been intended for reinforcement for Africa, but never made it. My observation was, with Tunisia secured in December the Joint Chiefs can take much more seriously the proposal for a March invasion somewhere else. What the Axis have would be reflected in what never reached Africa in December. How they redeploy those forces depend in a large part on the already proven effectiveness of British Deception operations, and Italian/German disagreements.