Unfortunately, the answer isn't the same in both cases.
Typically, a full-frame camera is better for landscapes because of its improved dynamic range and wide field of view (using an equivalent lens).
For wildlife, crop-sensor cameras tend to be attractive choices because the crop factor helps you fill the frame with your subject more easily (again, using the same lens). It's important to note, though, that this is really just an *apparent* magnification of the subject.
I'm not sure how much of this translates to brands other than Canon, but for the reasons above, Canon's top-end crop-sensor cameras tend to feature great autofocus and high-speed shooting capabilities that appeal to sports & wildlife photographers, whereas their lower-end full-frame cameras offer great image quality for landscape & portrait photographers, but give up a little speed. Remember that these are really broad generalizations, and individual cameras often stretch those stereotypes a bit as new technologies are introduced.
By the time you get to a pro body, it's assumed that you'll be able to afford the big fast glass needed to reach wildlife and sports subjects, so those pro bodies that have full-frame sensors (this hasn't always been the case, btw), will tend to also have top-notch autofocus and high-speed capabilities.