[schuyler2d]

Well the evidence is circumstantial. A bunch of Canaanites celebrate a spring festival with unleavened bread. Later they adopt a different religion that has a spring festival and an Exodus story with a new god called YHWH is glommed onto El.

I think it depends how "natural" one thinks the reason for unleavened bread is to Exodus. There's obviously plenty of mythical aspects to the story but the oldest are more focused on the river (Song of the Sea) and the battle. Why not combine rebirth/reinvention stories -- one a feast and another the beginning of "freedom"

But it's fair to say that most of Passover as a story and holiday is unrelated.