Hi Martin
I don't think any single lens is going to excel in these three fields. You could argue both would cover portraits, the 17-55 better for landscapes and 24-105 for wildlife at a push!!
In saying that, and there is never and absolute correct focal length for the task at hand, you might be better with a 10-22, 50, 70-200 /100-400 but thats gonna cost a fair bit.
If I had to choose one for the crop...17-55, aperture aside I think it would do portraits/landscapes better than the 24-105 could do portraits/wildlife.