Well that's speculation, it's hard to judge how a woman influences a man. Michael had been cold and calculating and feircly independant. I don't think Kay influenced any of that and anything else that happened due to this is IMO his doing. Kay to me was a wise choice, she counterbalances his tendancy to get seduced and sucked into the lifestyle. But regardless I think Mike would always have strived to be legit, Vito did as well and her influence wasn't as much of a determining factor but more of encouragement.

He even went legit after they divorced. As for Apollonia being a similar influence. Well I don't know if she would have instilled compassion within him. I doubt Michael wouldn't have changed much, but he definatly could. I think he would have changed less Apollonia would have been more submissive than Kay and Michael would have a greater perpensity to fall back into old hanits. I think perhaps Michael would parralell his father a bit more if he had a Sicilian wife though, psychologically.

It's overtly elluded to in GF II that Michael's main failing is he lost touch with the common man and has turned to grasping for power at whatever cost. Vito always kept his compassion about him and he always had this common touch and this is a major seperation of the two. However by GF III, you can say Michael has regained at least some of this touch. But you do raise a good question, the relationship of Apollonia and him may have resulted in a different Don indeed.