You have to provide some of the above mentioned documents that are applicable to your uncle in Canada and regarding Birth certificates of your Uncle, you can attach an affidavit stating your relationship with your uncle if you dont have any other proof.
Letter of reference is important and compulsory,
But in addition to this your Pay stubs, ITRs, Increment approvals and work Contracts are optional and more proofs u give to CIC better satisfied they are about your being working in past.
I am not sure but if you want you can check ur eligibility by clicking on the first link of the FAQs mentioned on first page of this post.
Best of luck