I know it is thought to be Ramses II but we do not know for certain. We have so much historical record of the time period from numerous sources. I know many pharaohs would destroy evidence of their predecessors such as removing cartouches etc, but surely there must be some record or reference. Why is it so difficult to be certain?
We have so much historical record of the time period from numerous sources. ... surely there must be some record or reference.
We have lots of records for some kinds of things. We have only one source of information for the story of the exodus, and that is the book of Exodus. And since our only source doesn't identify the pharaoh, no, there's no record or reference. There's no other evidence for the story.
(Evidence for cultural links between Canaan and Egypt, yes; evidence of Egyptian control over parts of Canaan in the time of Ramesses II, yes; evidence for an enslaved culture-group in Egypt, no; evidence of a mass migration of enslaved people, no.)
Two previous answers on this subreddit go into much greater detail about key aspects of the question:
In this response from June 2020, /u/Antiquarianism presents an argument that the Moses of Exodus is a composite culture hero, and pointing out that there's no evidence of a culture-group being enslaved in Egypt or Sinai.
In this response from March 2021, /u/ScipioAsina collects some indications of why the modern imagination has picked Ramesses II as its favourite for the pharaoh of Exodus. To their points I'll add that Ramesses II is simply far and away the most memorable pharaoh of the New Kingdom, partly because he had such an exceptionally long reign.