I don’t know where your information is coming from, because the only “source” for “Channing has talked about dating dudes before” came from tumblr user barringtonhigh (since deleted). This person then posted something along the lines of “when you try to prank tumblr except you’re right” – except the “proof” that they used to prove they were “right” was a single article about Channing checking out fellow dudes on the set of Magic Mike, which was clearly a joke. So it was absolutely a prank by barringtonhigh, which was then “validated” by a jokey comment from Channing Tatum.
Literally, show me a single valid source where Channing Tatum explicitly says “I have dated men” and I will take it back. But you can’t. Because it doesn’t exist.
I agree, more bi actors being out would be fantastic. But fangirl over Alan Cumming or Evan Rachel Wood or Raúl Esparza or whoever, not Channing Tatum. Even if Channing Tatum turns out to be bi, he’s not out, so spreading the rumor that he’s bi isn’t helpful regardless of whether he’s straight or bisexual.