The problem with the attempted fix on the PRE as I understand it is that the government is only attempting to establish the tax liability, not prevent the absconding of proceeds of sale funds immediately after the disposition of the property.

Taxpayers only need to file in most cases, by April 30th in the following year.  If a property is flipped by a non-resident buyer, then the lawyer or notary for the seller should be required to keep a holdback equal to 25% of the gain on the sale in trust for tax purposes.  That way, the MNR does not have to go hunting for  the funds a couple of years after the non-resident sold the property.