Unity 5 UI GUI Text Canvas Screen Resolution Adaption Problem

Don't do what you suggested, is a really unflexible way of doing what you want.

Checkout the "UI scale mode" property of the Canvas Scaler component in your Canvas game object. It defaults to "Constant pixel size", a really bad option if you aim to more than one resolution, a window of 640x480 will only show a 640x480 rectangle from the top left corner of your canvas.

Change the UI scale mode to "Scale with screen size" and unity will shrink or expand your Canvas to best fit in your screen.

FOR ANYONE WHO HAS THE SAME PROBLEM, LISTEN CLOSELY. ALL YOU NEED TO DO IS: Canvas -> "Your Text" -> Settings sign on the top right -> Reset

Then Under Rect Transform You: Anchors -> Min X: 0, Min Y: 0.5, Max X: 0, Max Y: 0.5

Then You: Pivot X: 0, Pivot Y: 0.5

When you do so, the top left square in rect transform should say on top: Left, and on the side: Middle. Then you may move your text/buttons anywhere you like. (Note: Anywhere in the canvas.) Make sure your Scale is X: 1, Y: 1, Z: 1. To resize your text, use the font controller. If you follow my instructions, when you play your game, (in the editor to test) you should be able to change the ratio from your game view to Free aspect, 5:4, 4:3, etc without losing view of your GUI text/buttons/image/etc. (PLEASE NOTE: Maximize on play MUST be selected.

Hope this helped since I know this is a big problem and I even had this problem myself.

Happy developing :)