I am having the same problem. I want to make a menu with predefined resolutions that the user will be able to use if he or she have performance issues, but using the "set canvas size" in combination with letterbox scale aligns the canvas in relation to the top left and not the center of the screen.
I would have imagined that the set canvas size exists for that reason, yet it renders the whole thing useless since you have to manually scale the browser's window afterwards, in order for the letterbox scale to catch up and realign the project to the center.
I really want to avoid this for both aesthetic and presentation reasons.
The iFrame solution that zatyka mentions does not work in my case.
This behavior is consistent with node web-kit as well.
Dear Ashley is there a plan to address this issue and, since it has being around for some time now, is there a workaround to this?