Image - Canvas Size would, in every version of Photoshop going wayyy back, change the size of the canvas WITHOUT resampling the pixels to fit. Thus if you increased the size of the canvas, it would add blank space around the edges. Please go back and double check the older versions; you'll find I'm right. Nothing has changed in the Canvas Size function in Photoshop CC 2014.
If you want to change your image to a larger size, you need to use Image - Image Size. Whether you want to resample or just change the ppi value is up to you - the [ ] Resample Image checkbox affects that.
-Noel