Sea water is corrosive! So letting it dry on its own may have cost you your camera body!
The first issue is leaving the batteries installed so even if the camera is off power is still going through some of the circuitry so with a bit of sea water you have electrolysis taking place effecting the exposed metal surfaces of the circuitry eroding them. Then you have the chemical corrosion aspect and the shorting of electrical paths that can't sustain the higher voltage.
At this point you'll need to find a good camera repair person who knows this camera or send it off to Canon. I'm not sure if Canon we repair a water damaged camera and as the Rebel series is their low end models the cost of the repair make get close to the cost of getting even a used Rebel to replace yours.