I (reluctantly) watched the first 4:40, then I stopped, because his reasoning is crap. For no apparant reason the UK government locates to Canada the 4th of june. Then he starts talking about Geremany launching Sealion, surprising the British by ignoring the peace treaty (and he shows the barges the Germans were planning to use it).
Well, that is just crap. Even after a total failure at Dunkirk, there's no reason at all for the British to relocate their government to Canada at the 4th of june 1940. Any PM who would suggest it, would be out of office very soon. There is literally no way that the Germans can surprise the British with Sealion. The barges needed to be shipped to the ports at the Channel. You can literally see that happening standing at the cliffs of Dover. This shipping takes time. The German forces need time to reorganize after the battle of France, this takes time too.
So after the fall of France, the Germans need some time (I guess several weeks at minimum, but a month or two is more likely), to make their preparations. All this time the British can see a part of these preparations with their own eyes. And even if they ignore what they're seeing, it still doesn't lead to a succesful Sealion, because if the Germans don't destroy the RAF first, and gain airsupremcay (airsuperiority won't cut it), they're still screwed. Because even if they get some divisions across, which is highly doubtful, they'd be cut off by the RN then, and will only last a few days, a week at most.
So yeah, his reasoning is crap. The video might be entertaining to watch for you, but it is very poorly researched.