Where do you plan to sail?
If you get an iPad, you'll want to have a waterproof case (Targus makes a nice one). The screen is covered by a non-glare surface, so visibility is better. The down side is leaving an iPad in a case in the sun will cause it to over heat and shut down to prevent damage.
If you are going to stick to sailing around Ottawa or the Thousand Islands, I don't see a real need for a chart plotter. I sailed in the 1000 islands for 30 years with just a compass and later a compass and handheld GPS. The Richardson's Chart book is worth having.
If you opt for the iPad be sure to get a cell phone capable iPad. The GPS chip is integral to the cell chip, the WiFi only models don't have gps, they rely on wifi data. Doesn't work well.