This is a really fascinating video that mentions that there was one match-up of DC and Marvel that is considered canon.
https://www.youtube.com/watch?v=MisAkBx0u7E
Such an idea interested me, so I decided to do some research, and came to this very interesting page.
https://www.quora.com/Which-comics-a...ossover-series
Here are some excerpts of what they give as evidence for canonicity of certain crossovers...
Spider-Man and Batman(1995)
In the later DC vs. Marvel (considered canon, apparently) Spider-man(Ben Reilly as this was during the Clone Saga) sees Access and is accidentally teleported away to Gotham in front of the Joker. Joker recognizes him and points out the new costume(referencing the events of the previous Spider-man/Batman crossover, though Joker has occasionally made references to non canonical events,likely due to his insanity.)Spider-man says he’s never seen him before(which makes sense since it’s not Peter Parker).
Green Lantern/Silver Surfer: Unholy Alliances (1995)
Kyle Rayner designs a logo for a coffee shop in this series which we see late run the canonical series. In the comic Parallax: Emerald Knight, Parallax mentions having chased Cyborg Superman: “across the universe and even into another”. The character Access makes an appearance and he is important later. In Extreme Justice #18 Blue Beetle uses a "fibrous polymer" to entangle two opponents which will "dissolve in an hour or so", and explains he "got the recipe from this guy who just drifted through from some alternative universe recently", referring to Spider-Man. However this is ignored in the other canonical crossover JLA/Avengers.
DC vs. Marvel (1996)
The character Access is introduced as a being connected to both universes:
JLA/Avengers (2004)
The site just randomly says that this is a canonical crossover.
There is also apparently something called Crossover Earth, which is where these titles take place...
Uncanny X-men and the New Teen Titans(1982) (this features Darkseid and Thanos, so is it officially what ScrewAttack was talking about?
Batman/Daredevil (1997)
Batman & Daredevil: King of New York (2000)
Thoughts?