The canvas in CC3 is basically unlimited. All you have to do is to delete the entities on the MAP BORDER layer (The drawing tools uses the entities on this layer to determine where to "stop"), then draw a new rectangle on the MAP BORDER layer where you want your new map edges to be.
Or you can rescale the entities on the MAP BORDER layer (freeze or hide all others) either with SCALE or SCALEXY, the latter seeming more adapted to your case. If you want to expand north (I assume it is upward), select all the MAP BORDER layer entities, type SCALEXY, enter 1 for xscale and for exemple 1.30 yscale to add 30%. Select the lower left point to expend up.
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If you want to expand north (I assume it is upward), select all the MAP BORDER layer entities, type SCALEXY, enter 1 for xscale and for exemple 1.30 yscale to add 30%. Select the lower left point to expend up.