“I don’t know if it’s for me to say… We’re picking up so many years after the events of that movie, maybe a coda is a better word than sequel.”
Canonically, Routh’s Superman is the same Superman from Superman: The Movie and Superman II (director Bryan Singer thankfully ignored III and IV), the Superman who reversed time, made Lois Lane forget his identity with a kiss and lifted an entire continent made out of kryptonite into space. Christopher Reeve’s portrayal, and by extension Routh’s, was essentially modeled after the character from the Silver Age. This is an older and more powerful version of Superman than we’re getting on the CW’s Supergirl. It’s the most iconic and beloved version of the charactor. No, Routh isn’t Reeve, but he’s playing that same version on Crisis, the same Superman who went through the events of Superman I, II and Returns.
Superman The Movie is a significant film. It was the first major comicbook movie and paved the way for the entire genre. In the same way that Earth Two Superman (Kal L), the original Superman from Action Comics #1 was given top billing in the Crisis on Infinite Earths comic book series when he took the lead in defeating the Anti Monitor, so will likely the Reeve/Routh Superman. In other words, it’s reasonable to conclude Routh’s Superman will be the key to defeating Antimonitor in the CW’s upcoming multi-hour epic.