Better, though I got distracted by trying to calculate the relative sizes of the giant seas, the planets, and their distance. Expect an observation on that soon.
Anyway, by word of GM the plane is 20 miles deep. Off course, the giant lakes don't go down to the bottom, so let's assume they stop at 25 km. Nice number, and rids of that archaic nonsense that seems to be preferred in some parts of the world.
Assuming the planets are terran in size, they have a volume of roughly 1.×1021 m3. Assuming again, that the lakes are a perfect cylinder, that gives us a radius on the scale of 109 m. So said lake would be about a million kilometer across.
Now, as our overgod has said that the planet can easily be seen reflected in the water below. This means that the sea, seen from the planet's pole, is still quite big. For 5 different scenarios.
a: The sea practically covers the entire sky (visual angle: 179.9 degrees) 17 000 km (Very approximate number)
b: The sea nearly covers the entire sky (visual angle: 160 degrees). 175 000 km. (Very approximate number. )
c: The sea covers a large part of the sky (visual angle 120 degrees) 575 000 km (Very approximate number)
d: The sea covers half the sky (visual angle 90 degrees) 1 000 000 km (Very approximate number)
e: The sea covers a small part of the sky (visual angle: 45 degrees) 2 400 000 km (Very approximate number)
Note: if the planets are larger, these calculations will be massively inaccurate.
Edit: Never mind. Internet is better, but now browsers are acting up and randomly crashing. Really should check this computer completely sometime. Action up soonish.