To reproduce:
1) Upload attached build to a server (loading from file causes it to never load)
2) Open Build\UnityLoader.js
3) Notice in line 202 it is 'Module.canvas.id = "canvas";'
4) Open the uploaded build in windowed browser

Expected: Try resizing window - notice it resizes content correctly

5) Change the id to #canvas
6) Repeat step 4

Actual: Try resizing window - notice that content doesn't resize with window but stays the same size

Reproduced in Chrome 57.0.2987.133 (64-bit) and Firefox 52.0.2 (32-bit)