I tried using a few quick sketches as alphas, but I can get rid of the canvas border. Is this even possible?
i think there is a border label in Document Tab. just select the desired color you want then click both Back and Border to change the background. and resize your document.
what do you mean the canvas border?
there is canvas border in the document, i’ve notice that when i turn the background color to white.
Heres my prob…I paint a simple texture in quick sketch, and I want to use the drag and drop tool to place it on my model. But when I do, it looks rectangular because of the border. Is there a way to I guess feather the edges of the rectangle?? I want it to work like the default alphas in zbrush. you dont see a rectangular border when u use those
How about filling your quick sketch with black and paint on that in white or grayscale? 
Hope that helps.