Now that I think about it, I suppose logistically they could interview every aspiring tourist at a Canadian embassy before issuing a visa. But then again, we need more staff at Canadian embassies who know the local language so that they can interview each person. While we could pass the cost on to them through an interview fee, that could discourage tourism to Canada. Add to that that other countries could reciprocate, just like Brazil required US citizens to fingerprint at the airport after 911 when the US imposed that.
And that still leaves us with how to ensure an officer does not make his decision based on prejudice and, more importantly, how to ensure that this values test doesn't teach people to lie about what they believe.