1)  Flipping is a business, not an investment, and should be taxed as business income, and not as a capital gain. I believe that this is the rule now, in theory.
2)  When foreign buyers sell property there should be a withholding tax on the principal sufficient to cover any taxes, business income or capital gains, forcing the proper filing of a Canadian tax return.  If it is claimed as a principle residence, proof must be provided that the property was used only as a principle residence, and that the owners were in Canada and occupying the home for more than six months in each year of ownership. (confirmed by CBSA),