Other mistake: When Gary is about to test the trap check the bus door on the right: there's a reflection of what seems to be his shirt, but it's a long sleeved wrinkled shirt, not the short sleeved he's wearing. What's even more bizarre: when Gary moves around, the reflection stays completely still and, drumroll, a shot later, from the very same angle, the reflection disappears. Either it was a crew member hiding, or a CGI-made reflection placed to hide some unwanted crew or equipment reflection.
Other mistake: In Walmart, some mini-Stay Puft Marshmallow Men turn on a propane grill and set each other on fire. Gas grills on display never, under any circumstances, have propane tanks installed. This would create an obvious safety issue because there is nothing keeping a customer from accidentally (or deliberately) starting the grill and causing a fire. Additionally, propane tanks are never stored inside for similar safety reasons.
Other mistake: When Trevor attempts to start Ecto-1's engine the camera shows a very incorrect engine. A Triumph Herald/Spitfire 4 cylinder that is less than 1 to 1.5 litre.
Other mistake: Egon's old jumpsuits fit the kids perfectly, but he was a grown man and these are young children.
Answer: Yes, it is still canon. Director Jason Reitman has confirmed it is, and there are actually lots of easter eggs referencing it in "Afterlife." For example, Ray still has his bookstore from "Ghostbusters II." The "dancing toaster" is in the farmhouse. Etc. They chose not to directly reference it in dialogue since it didn't have much to do with the plot, but there are plenty of hidden details confirming it is still canon. Reitman has also said that there are plans to possibly bring back more plot/characters from "Ghostbusters II" in the future. (It just depends on what direction the sequel ends up going in).
TedStixon