It is a PITA but can be done. I used to install stereos many years back. You basically have to remove the seats, carpet, and door panels, then install a sound deadening mat in those areas. Someone mentioned Dynamat, it is a good one but there are cheaper mats that can do a very good job. Google sound proofing car and you will get many ideas. Be ready to put in some work. There are professionals that will do it for you. I don't know about Toronto area. The aftermarket stereo installation has dried up everywhere since carmakers have upgraded their sound systems. Gone are the days when you could buy a car without a radio and put your own in. But fear not it can be done and the results can be amazing. You can also put some material under your hood to deaden the sound of the engine. Putting it in the doors gives your car a nice thump, think German, when you close the doors. You could go all out and put it under the headliner, but that poses many problems and newbies should stay away from this. But if you have basic mechanical knowledge and perseverance you can get great results. Good luck!