This is in the checklist for Buffalo:
5.
PROOF OF RELATIONSHIP IN CANADA (IF APPLICABLE)
Submit:
•Proof of relationship showing you have, or your accompanying spouse / common-law partner has a close relative who lives in Canada and is a Canadian citizen or permanent resident. This close relative can be:
•parent, grandparent,
•child, grandchild,
•brother, sister,
•aunt, uncle, or
•niece, nephew.
•Proof of relationship to your close relative in Canada, such as birth, marriage or adoption certificates. For example, to prove that your relative in Canada is your paternal aunt, it would be necessary to submit copies of birth certificates for her and for your father showing they have at least one common parent.
•If your close relative is a permanent resident of Canada: provide a photocopy of his or her Record of Landing (IMM 1000), Confirmation of Permanent Residence or Permanent Resident Card.
•If your close relative is a Canadian citizen: provide proof of Canadian citizenship, such as a photocopy of pages of a Canadian passport or Canadian citizenship card.
•Provide evidence to show that your listed relative is currently residing in Canada. This may include copies of:
•lease agreements,
•a current Notice of Assessment from Revenue Canada,
•an employer's letter confirming employment,
•monthly bills etc.
Note: The evidence should show the relative's name and full address in Canada.
I don't know what you already sent but it looks to me that you need at least yours and your sisters birth certificates showing that you have the same parents, a copy of her PR card or Canadian passport and some proof that she is residing in Canada.
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