Pretty sure this FTC will try to block the merger, and I feel like it will be one of their better cases against consolidation that they have filed lately.
Disclaimer: I'm not a lawyer but I do have a friend that is one and works in one of the govt agencies on antitrust stuff and we've had long conversations about the topic.
The standard for antitrust in this country right now really is solely focused on
consumer welfare (for better or for worse). And a merger will only be blocked if the govt can demonstrate that consumers will be significantly harmed by that merger and the consolidation it brings. So like if a SF pass is $150 right now and a CF pass is $150 and there's reason to believe that a combined pass would be like $600, that's pretty clearcut. I don't know if you could make a strong argument that it will do that. More likely the companies would say, "well now you can get a pass to both groups of parks for only $200 or we'll include it in your passes you already pay for so it's a benefit to consumers!"
The FTC circulated a draft of
new guidelines which closed its public comment period a month or so ago that expand the standards for antitrust beyond just consumer welfare but as far as I can see it hasn't been implemented yet. Even under those guidelines, I struggle to see how this would be a slam dunk for the FTC. Like others have said, there's real competition between the two in only a couple markets: Philly-ish (Dorney & SFGAdv), NorCal (SFDK and CGA) and SoCal (SFMM and KBF). The CF/SF lawyers will point to all of the other theme park companies, some of which are much bigger and better attended than SF/CF and say that it doesn't "substantially lessen competition or tend to create a monopoly" as point 13 says on that list.
I could see maybe being forced to divest one of the competing parks in each market, although CGA, my local park, is planning on closing in the next decade anyways so that problem solves itself. For whatever it's worth, I'll believe this merger when I see it since we've seen so many of these news stories of X chain wants to acquire Y other chain that don't go anywhere but if it does happen, I'd bet good money that it will go through with potentially only minor modifications and divestitures.