well not really if I understand your question.
You can set maximum image width height dimensions in upload options and play with those to achieve a maximum width or height you want however you need to think about the actual image.
If an image is portrait or landscape that aspect ratio has to be maintained to show an image without distortion if you follow me.
if an image has say a ratio of 1:1.25 or 1.25:1 then the resulting created medium image would be in that ratio. Doing anything else would be considered a huge bug as no one wants distorted images in there gallery.
There is one new feature I would theoretically add in an upcoming version although I do not know how popular it would be. That is taking the same technology we use on the uniform thumbnail feature using Imagemacick which takes a center crop of the image and makes a square thumbnail. We could do a center crop as the medium although like I said not too sure how many people would use it. I guess you can make a suggestion in the suggestions forum and see how many others would think it useful.