To increase the font automatically when the canvas screen changes,
in the font size of the control you need put this formula
Switch(Parent.Size, ScreenSize.Small,12, ScreenSize.Medium,18,30)
so the font will be 12 in the small screen and 18 for the medium screen otherwise it will be 30 ,and you can change these font sizes to your desired font sizes.
You can use variable to apply these for all controls
On the screen onVisible property we will set a variable for the font responsive size we need and use it in the controls we need to make its font responsive.
as the canvas app is not responsive by design and there isn't one place to apply for all the canvas but variables make it more easy instead of writing the whole formula every time.