Is there any connection between Stranger Things and IT movie?
Yes, IT is one of the inspiration behind the show.
The Duffer brothers, who actually once pitched an “It” remake themselves, recently told Vulture that the connections are completely intentional. But there seems to be one big hole in the theory.
“Stranger Things” co-creator Matt Duffer first told Vulture that he
had a problem with the 1990 “It” miniseries as a kid, and Bob’s story
was inspired by that.
“I think [Bob’s clown story] was really me describing something that
just freaked me out. I didn’t have that experience myself. I just had
nightmares like that,” he said.
“I’m sure we were just like, ‘It would be cute if [Bob] suggests moving to Maine, right next to Stephen King.’ Stephen King exists in
this world. Some of the characters have read Stephen King. But Bob
definitely does not read Stephen King. He’s not interested at all in
Stephen King because he hates that kind of story.”
Is Stranger Things and IT is in same universe?
No, Stranger Things is inspired for so many 80s famous things,m it's not canon to them but play a homage to them.
Even Finn Wolfhard play different roles: Mike Wheele in Stranger Things and Richie Tozier in It (2017), saying same dialogue is more of easter-egg/reference only.
Even Mark Hamill said a Star Wars dialogue in Flash, still Arrowverse is not canon to Star Wars
Related post: Meaning of Mark Hamill's “I am your father” line from The Flash