Margins ?
At script level, page and canvas are reported (at least on my system) to be the same size ...
Code:
tell application id "OGfl"
tell front canvas of front document
set {lstPage, lstCanvas} to {page size, canvasSize}
if lstPage = lstCanvas then
display alert "Page and canvas are same size"
else
display alert "Page and canvas are different sizes"
end if
end tell
end tell