That's a fair question. The Consumer Price Index only provides data in aggregate form from a basket of retailers. The Statistics Act protects against the disclosure of specific data points. The consumer price index is important to track inflation affecting Canadians at large, but it isn't very useful for analyzing specific pricing trends.
I believe the organizer of this effort is specifically looking to find instances in which grocers and players within the grocery sector increase prices for non branded goods at the same time, which implies collusion. Think for example, bread price fixing and when they break the promise of not raising prices for x number of months. They wrote down a few analysis ideas to that effect.