All the ways in which you will care about how to buffer dimensions of your canvas to avoid aliasing artifacts can be handled with just the window.onresize event, whether your canvas is fixed or proportionally sized.

https://codepen.io/SeanMcBeth/pen/QWOoLNX

Throw a check in there to make sure the native dimensions actually did change so you don't needlessly redraw. Debounce it with setTimeout if you're super worried about people waggling their windows around or whatever.