If you have reason to periodically be in LHR, you can get a discounted business fare on AC from LHR to SYD for $6,500 which allows a stop-over in YYZ each way for as long as you want. Buy a positioning flight to/from YOW to LHR for <$1,000. $7,500 gives you two trips to London (one in J) and one to Sydney. Pretty good value IMHO.