that's a possibility but it isn't actually likely, Dreamworks only did that to Road To Eldorado because the MPAA put pressure on them to at the time
but if the MPAA okayed the gay reveal in Paranorman, the acknowledgement of Same sex parents in the Boxtrolls and Storks, and retconning Lefou as gay on Beauty and the Beast (which kinda blew up in Disney's face but I digress) it might not be out of the question for there to be a subtle hint that Harold isn't straight in the Captain Underpants movie, not specifically that he's Gay but it's actually more likely they will just not say either way whether he is gay or straight and just not bring up romance period