Fixed aspect-ratio MobileCanvas and orientation

I’m a long time xojo desktop app developer but newbie IOS developer coming up the learning curve (whew!). I’ve figured some stuff out but am currently stumped as to the best way to resize a MobileCanvas with fixed 4:3 aspect ratio to maximally fit the screen when the orientation changes. I’m using the AutoLayout scale factor to set the Height to 75% of the Width but then I’m stuck because depending on the orientation either the Width or Height should be the primary control of the object’s size.

I’ve tried using two canvas objects, one for Portrait and one for Landscape and control their visibility based on device orientation (and also use that to trigger the repaint in the visible object). But is there a better way?