According to the document link you sent and according to google search, for mobile phones best resolution for canvas is w:640 * h:960 …
this resolution is an example in the document you sent.
All is good but not perfect.
all game engines have the same rules of canvas + widgets components.
and there is no exception.
I am testing cocos creator 3.0 preview 1, learning typescript to use cocos creator.
canvas and widgets is always a trouble.
clearly a smaller resolution according to W:640 * H:960
and if it is larger
there will be a weird gap.
however, the widget is doing its job.
but UI positions will be different from mobile to other
still, I am not fully satisfied with this canvas