Your uncle can explain you and his relationship in his letter .
what his letter should contains.
1. explanation of your relation with him (family friend from your mother or father side , know you since you're kid and decide to help you financially to study in Canada etc)
2. He can write that he would wire you specific amount every month /year/semester (as detail as ) he can .
3. if your uncle is willing to pay a tuition for first semester before you apply for SP, it would be helpful.
even if he would not, still his letter and proof of income would also good.
4. if you would not present your father as a sponsor, then don't think it is necessary to send his land evaluation.
good luck.