Well, it better keep going for another five years after that, and then another five years after that, and so on, because anyone buying a $5 million 4-bed-2-bath house for their family is only more dependent on that trend continuing than the one who paid $2 million. The price tag is only justified when there's no end in sight to the appreciation. Nobody would pay $5 million for that house if its value stops rising, let alone starts dropping.
The government can't guarantee real estate, because any 99.9% risk-free investment with 10% annual growth can be levered into a 99% risk-free investment with 100% annual growth, and that's going to absorb all available capital like a black hole. The more the government acts to reduce risk without offsetting that by reducing returns or increasing the cost of debt, the bigger that black hole will grow.
At some point, it might be worth biting the bullet and incentivizing investments into sectors of the Canadian economy that aren't housing. If workers can see housing appreciating by multiples of the median salary, and entrepreneurs clue in to the fact that they'd earn more as a real estate agent than by building a tech company, "the Canadian economy depends on housing" becomes a self-fulfilling property. A few more doublings and then there's no point bothering to do anything else like growing food and assembling cars. Then you end up with a Zimbabwe situation where, yes, your house is worth a trillion dollars and rising, but it's not... good.
But maybe if we keep pouring enough gasoline on it, we'll be able to put out this fire?