..I see nothing wrong in your documentation, but when your uncle wrote to support you, did you show any of his financial documet or his employment letter?
The your bank statement(s) shows a huge sum deposited into it once or a breakdown of a normal regular transactions? if your bank statements shows a once huge deposit, the VO might think its a borrowed funds or not yours which was deposited for visa purpose
since you already on visitor visa, and records shows you have extended your stay once, then who were you visiting and what convincing ties to the people you visiting in Canada did you link to them(I.e are they PR, employed, tax payers etc)
As your family in your home country, what proof did you show that makes the family ties authentic(I.e birth certificates etc)
What immigration means by family ties in Canada and your home country is that you showed a weak home and Canada ties which was not convincing to the VO
In your SOP, how did you explain yourself, your family ties and reasons you decide to apply for a study permit instead of coming back home when on a visiting visa.
you can share your SOP let me go through it if you want..
johnpfyfasnow@gmail.com
Once a VO is suspicious of your application, they just pick reasons close to why they think you are been refused direct or indirectly
Since your uncle and you are in Canada, if your uncle is a PR holder, he can request the gcms note for you for $5cad or if he's not, you can get an immigration lawyer or someone you know that has a PR to request it for you.. you can request it yourself if you not a PR holder
To beginning or before you do anything regarding your SP, request for your gcms note