First, make sure you bypassed your factory amp (if so equipped) when you installed your deck. It's a POS that mostly produces distortion, and any decent aftermarket deck will produce more, clean power.
With $600, I'd get a 4ch amp, some custom components for up front, and a single sub in the trunk.
Run the components with the amp's front channels, and bridge the rear channels to your sub. You can either disconnect the rear speakers or just run them off of your deck.
Maybe some fellas from the great white north can make some suggestions on specific items due to the whole tax, shipping thing.
BTW, any snow up there yet?
