Seeing Vincent Schiavelli’s name reminds me of very awkward moment in live TV where Ryan Seacrest was asking Jeffrey Tambor about a movie he was in when it was actually Schiavelli in the role.
The movie was Ghost
Speaking of Gene Hackman, I sat all the way through the blind man scene in Young Frankenstein thinking “Boy, they really aged up Robin Williams convincingly!”
Dylan McDermott and Dermot Mulroney, whose similarity prompted at least one Saturday Night Live sketch, and I’m pretty sure the two of them even showed up together on SNL at some point after to extend the joke even further.
Lee Marvin and James Coburn.
Steve McQueen and Paul Newman
Me too! 
A sound-only example: I distinctly remembered Zooey Deschanel voicing Audrey in The Lorax, but it was actually Taylor Swift.
‘Ever confuse one actor for another?’
All the time. My wife never knows whether I’m joking.
We have this discussion all the time at our house, but it usually goes something like this:
My wife: Hey, isn’t he that guy?
Me: What guy?
MW: That guy that was in that movie! You know…that one.
M: Him? No, I think he’s the other guy, the one we always think is THAT guy.
MW: Are you sure? I think HE was in the OTHER movie.
M: I dunno…they all look the same to me.
I always confuse Edward Norton with John Cusack. They’re both about my age, we’re all Gen-Xers, and I saw both in many films, and when I think back of those films, I never remember exactly who of both played in it. I know they don’t really look alike, nor do their names have a resemblance, but my confusion is real.
Me too! They’re absolutely the same person.
I remember when I was watching The Sopranos for the first time. I found it a little odd that Brent Spiner was playing the role of an Italian mafioso.
It took me a while to figure out that it wasn’t this guy
playing Furio Gunta, it was this guy
who is Italian-American actor Federico Castelluccio.
Watching the end credits for Blues Brothers 2000, I was surprised to learn that the impressive female vocalist in the Louisiana Gator Boys was Koko Taylor and not James Brown in drag.
Jennifer Holland (Peacemaker), Vanessa Kirby (Fantastic Four) and Desi Lydic (Daily Show)
Also: I saw a photo from an article about an actress from The Rookie who died and thought it was Bridget Regan, who plays Monica. It was Annie Wershing who played serial killer Rosalind Dyer.
And speaking of The Rookie, I can never tell the difference between Shaun and Aaron Ashmore. 
For me, it’s Vincent Schiavelli and Richard Libertini.
And James Franciscus, James Farentino, and Tony Franciosa. Yeah, they don’t really look alike, but try to remember who was in what film!
James Franciscus was in Longstreet and that teacher drama show from the early 1960s. Tony Franciosa was in A Face in the Crowd. I don’t remember anything James Farentino was in, but I remember he was married to Michelle Lee.
Which reminds me of another pair I always mix up: Bobby Darrin and James Darren. Both Italian singer/actors who changed their names.
The MST3K Gang once riffed on this in one ep.
Years ago hair guy Jose Ebert, whom I had never heard of, had an infomercial about some of his hair supplies. I thought to myself, ’ What is Taylor Negron doing an infomercial with a fake name?’
I cannot tell Javier Bardem and Jeffrey Dean Morgan apart, I’d have to rely on accent.
I can definitely tell them apart, but I want Keith David and David Keith to do something together.
When he was less well-known, Terry Crews did a video series about building a PC with his son. Of course he already did a “secret dork” thing playing an aggressive basketball player who loves Vanessa Carlton in White Chicks. A “bad” movie I unironically love.
Cavill also did the Witcher due to being a fan of the games if not the books. Some speculation he wasn’t happy with the changes, but I haven’t followed that internet drama.
Claire Danes, Kate Hudson, Bridget Fonda. I can never remember which one of them was in that movie from the 90s I just thought about when I’m trying to get to sleep.