Both are accurate. They are measuring different things.
The Teranet measures paired sales for homes, similar to the Case-Shiller Index in the US. The TrebNet measures all sales without looking to pair up repeat sales for any properties. Because outliers may push average sales figures up, the source I linked for the Trebnet data gives median numbers as well.
There are a couple of additional ways to measure RE property value and thus changes in value, as well.