Film At a certain point, I began to think of the MARVEL cinematic universe, which I favour because it's good, and the WB/DC projects a bit like political parties or at least with the sort of tribalism with which kids used to defend their favourite 8-bit computer with (a debate I was largely on the fringes of even then with my Acorn Electron during the Spectrum/C64 years and then owning a C64 while people were throwing STs and Amigas in each others faces).
Partly this is because the creatives, or actors at least, are almost choosing which of the big comic book franchises to join to the point and there's little or no crossover between them. As far as I can see, none of the cast of the Suicide Squad or Batman vs. Superman films has previous appeared in the MCU or vis-versa so it's entirely possible for us, or at least me to think of them as either being, "MARVEL" or "DC" and be otherwise disappointed if they've chosen the latter.
Rachel McAdams is a favourite actress, so when she says she might be in the Doctor Strange film, it's a relief because it means she's MARVEL. Finding Amy Adams in the Man of Steel was a shame because I like her too but she's hitched herself to DC (even if she was a predictably good Lois in an otherwise bad Superman film). It should be noted that anything pre-Iron Man or pre-MoS doesn't count so I'm still in hope that Anne Hathaway might play one of the Inhumans or some such.
Is it possible to guess if an actor will turn out to be MARVEL or DC? Maybe, maybe. When the cast list for Suicide Squad was released, I wasn't surprised by most of the names. Looking at other franchises for inspiration, Emma Watson feels very MARVEL, but Rupert Grint is clearly DC. Daniel Radcliffe could go either way. Greta Gerwig, MARVEL. Brad Pitt, DC. Cary Grant, MARVEL. Gary Cooper, DC. No idea why.