Effectiveness really depends on what the goals are. If the goals are to replace human contact tracing, I don't think it will be effective. If the goals are to support or supplement it, depending on the design, possibly there will be some usefulness there.
If the goals are to actually collect, indirectly, data that can be used in analytics for disease modelling, then maybe there will be some useful data collected, but that's a different message that needs to be sent to Canadians.
I think that understanding what it is we're talking about and what the goals are for using such an app is really important.