You would use anchors to position the widgets in a canvas at the desired locations, it’s not easy to do in 4.4, you need to understand the anchor structure, better in 4.5, but not good enough. Also in 4.5, there’s a UI scale curve you specify in the project settings that state how the UI scales at different resolutions.
Edit:
For context, anchors are normalized coordinates specifying where the widget will be laid out in the canvas,
min(0,0) max(0,0) would be the upper left corner. min(1,1) max(1,1) would be the bottom right.
Cheers,
Nick