Yes, unless you use the new AI options for Sealion, the game might be too easy. But if you do, you might run into some bugs. The event was created on the idea that the player might invade Britain after defeating USSR, so it takes into consideration many events for USA.I have played until the fall of 1940, and I see that the mod has already taken care of boosting the AI. A good mod.
That event is in dire need of some fixing. Historically, USA was unlikely to declare war on Germany if they invaded Britain. In fact, during the 1940 the isolationism in USA was prevalent and most americans were not even sure that Britain could resist to Hitler.
They do declare war if Canada is invaded, which is quite possible in this mod, as Italy usually sends troop transports to invade the undefended Canadian provinces, unless the English are quick enough to capture Italian East Africa.