Five cups of mashed or whole Strawberry?

I don't think it matters. You are going to be mashing it either way. Though mashing cooked strawberries is easier than uncooked.

I do have a pet peeve about the name of the recipe. This is a jam recipe. You would have to strain the mashed strawberries to make a jelly. From what I'm reading, strawberries are mashed then canned. Still sounds delicious.