For what it's worth, I'm in Canada and have been trading with Interactive Brokers since early this year using a friend's US address. They don't send anything by regular mail, so mail going to someone else's house isn't a problem.
I started with $5,000 US and agree that it's impossible to trade with a Canadian broker unless you have a very large account where $30 and up commissions each way don't have a significant impact. Daytrading with any size account also isn't a good idea with Canadian brokers, since they aren't direct access and your order execution would be so slow, it would be a real disadvantage. Plus you've got to actually phone in short sale orders and pay an even higher commission.
If you want to do this for a living, a professional firm is probably your best bet, but not until you've spent a lot of time studying so you really know what you're getting into. If you've got contacts and/or a good education you might be able to get in with a company where you don't have to put up much money, but you would have to move. Otherwise it's $10,000 US minimum, but you'd be hard pressed to make a living off that.
I've recently decided to do this for a living and have quit my job and moved and am joining a professional firm.
Good luck,
Corey