This request is related to the question posted here: https://forums.toonboom.com/harmony/support-and-troubleshooting/changing-canvas-size-stage-resolution-without-scaling-contents
Currently it is not possible to change the canvas size without scaling the content as well.
I compare this to OpenTOonz/Toonz Premium: the scene output settings are controllable for both: either changing the canvas size (proportionally or not) without scaling the scene contents, or changing the canvas size (proportionally or not) and the content scales along with the canvas size. Flash offers this option as well.
Having the option to change the canvas size without resizing the actual content is quite useful to have.