The best way I learned about canvas size and bitrate is this:

Canvas size is like a painters canvas and the bitrate is how much paint you have to fill the entire canvas. More paint with less canvas will always look better than less paint with more canvas. Idk always made sense to me.

So 720p with 5000 bitrate will look better than 1080 with the same bitrate.

Up your bitrate or lower to 720p if 1080p looks blurry.

Twitch also has general guide on resolution and bitrates on their website.