Sounds fun and I look forwards to trying them, thanks! While I appreciate you having a Canadian presence in Seelowe, it seems to me it's too small. There are two ways to approach it, game balance and plausibility. Game balance is pretty self-evident from testing, although to account for differences in player ability I'd need to have another game as the Germans to be confident. In terms of plausibility...
Compare the populations of the UK, Canada and Germany. Canada is the smallest for sure, but A : they were extremely motivated at the time, they weren't THAT small and a big chunk would enlist, and B : while German losses at that stage of the war were nothing compared to what they'd be in future, they had suffered losses. Additionally there was a need to hold down captive populations in Poland, France and elsewhere. It isn't as if winning means you can automatically reassign everyone to the UK front.
So my point is, in terms of scale, I find a dozen Canadian units entirely valid. Do they arrive all at once or are present at the start? No. I'm thinking once it becomes clear the UK is in trouble, THEN the colonies pitch in, or at least pitch in more anyway. To satisfy both plausibility and game balance, have transports start showing up on the western edge of the map around turn 6 lets say. Maybe 3 or 4 at a time, every six turns? Something like that perhaps, with a few German subs to make things interesting.
Don't quote me on this but I read that at the end of WWII Canada actually had the largest navy in the world. Maybe that's due to losses suffered by other participants and most of it being merchant marine, but still, if correct it would support my idea. Heck weren't at least a few of the UK aircraft built in Canada as well? Could have a fighter or three pop up as reinforcements.
I'll also say that a failed Dunkirk evacuation makes more sense as a precursor than a defeat in the Battle of Britain. It's difficult for me to see the UK losing the BoB for a variety of reasons, not least home field advantage. If German aircraft wanted to be able to fly home they couldn't afford that much time in the theatre of operations after all, certainly not as much as the UK. Plus if a German pilot bails out he can't return to the fight. If a UK pilot bails out he can. There are a lot of things working against a German win, it was an "ambitious" operation no matter how you look at it.
Dunkirk on the other hand was really only one order from the fuhrer away from failure. Hitler thought it was a trap and ordered the luftwaffe to hold back, which they did. Even so it was a near thing, a very near thing indeed. That an organization as proud as the royal navy had to call on and accept help from civilian vessels only proves my point. They never would have done so unless it was absolutely necessary and they had no choice at all, which they didn't. Now none of that is impacting on actual gameplay for the scenario, it's a quibble on my part really. I'm only adding it for potential purposes of a blurb at the start.
Anything and everything I've already said, everyone more than welcome to weigh in
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