Hey Sina,
Replacement screen is no big deal. Lots of places can replace the screen at a reasonable cost. The replacement screens in my experience are OEM quality and will last many years in normal use. I have an S4 and have replaced the screen and as well replaced screens on iPhones, iPods and a Galaxy tablet.
In the Mississauga area I suggest:
http://techknowspace.com/ <-- I really like this shop, I've had zero problems and their price is competitive. They also have a location in Toronto
http://www.techvilleonline.com/other-cell-phone-repair <-- I've not gone here, but several friends swear by them. Less expensive, better warranty and will do the work while you wait.
Most repairs can be performed within a few hours (actual work is <30 minutes) and have a warranty.
Be aware, screens are made up of multiple layers: protective glass, touch layer and display layer. For some products certain layers can be separately replaced (as in your S4), but in other products they are bonded together (iPods). The shop will make the determination and let you know. If it's just the glass on your S4, you are looking at ~$100. All layers is ~$200. At $200 you should consider if you want to get a new phone instead ..... up to you.
Did you get last week's lollipop upgrade? What do you think?