8.  Heavily tax vacant homes.
9.  Cross-check property values against the owner's names, see if any income tax is paid in Canada by the "owner" and that person's relatives.
10. Cross-check provincial property transfer tax records vs. federal income tax records to collect capital gains taxes owing.  Do this across the board - it is aimed at ALL tax dodgers, not just the immigrants/PRs/long-term visa "immigrants."
11.  (re your #1 and #2): You need a Canadian passport and SIN to own, and each SIN can hold 2 properties at most.  
12.  Shut down the ridiculous 10-year, come-and-go-as-you-please visa program.  Refund their money, quit issuing anything other than short true visitor's visas and student visas.