Oration cracking up a large area of Canada (7)
I believe the answer is:
ontario
'a large area of canada' is the definition.
(Ontario is a Canadian province)
'oration cracking up' is the wordplay.
'cracking up' indicates anagramming the letters (the original order breaks down or cracks up).
'oration' with letters rearranged gives 'ONTARIO'.
(Other definitions for ontario that I've seen before include "Smallest of the Great Lakes" , "vast lake" , "one of the provinces" , "Canadian province and Great Lake" , "Most easterly Great Lake" .)