The internet has been coming up with creative new ways to tie Frozen into the rest of the Disney universe. The most poignant theory being that Anna and Elsa's parents died whilst sailing to attend the wedding of Flynn and Rapunzel from Tangled and that the wreckage of their ship is the very on that Ariel explores in The Little Mermaid. An alternate theory has the ship wash up on an island where the parents die - but not before having baby Tarzan!
Others have found more tangential ways of linking Brave, Frozen, Tangled and The Incredibles together while stepping sideways over to Pixar there's this masterful post linking all of Pixar's work together.
But the thing is that Disney have been creating canon crossovers of their films for ages. In the Hercules TV series, they spent a full half hour having Jafar and Hades team up to take on each others nemesis, Aladdin and Hercules. The actual conflict is average, but it is fun watching the two villains compare and critique their approaches to evil.