You can trade through most of the large full service brokers on the TSX.
One of the problems is that you may need to place the order during Australian trading times whne the Canadian market is closed.
The Aust broker will then relay the order to a Canadian partnered firm or branch to carry out when the market opens there. This can make it difficult to control the price you want to trade at.
Most firms charge at least their standard full services brokerage of around 1% but I have seen some charge a premium on these types of transactions
