I would suggest "forgetting" the WiFi network on the iPhone, and reconnecting again. To do this, go to Settings -> WiFi -> Press the little "i" on the right of your WiFi network's name, then press on "Forget". Then simply connect again.
If the issue persists, I suggest rebooting the router (black device with the Videotron logo in front). Simply remove its power cable and connect it back in again.
If that fails, tech support can help: http://www.videotron.com/residential/contact-us