I would recommend not getting one from the wild, you never know what they may have in terms of parasites, diseases, etc. I'm not sure about the difference between a great pond snail and just your plain old pond snail, but the regular ones reproduce like craaaaazy and don't do much other than just exist in your tank ;) What about something like a Nerite snail? they can't reproduce in freshwater, and they're great algae eaters. They also don't get huge like mystery or apple snails can. Is your tank fully cycled? If so, it should be able to handle the bioload of one snail like a Nerite, when I had one in my 3 gallon 2-3 50% water changes a week kept the ammonia under control. I see you're in Canada, not sure what the selection is there but I can get these at Petco.
I feed mine blanched veggies and harvested algae (I do this by leaving rocks, water, and a dash of ammonia in a jar in the window, then swapping the rocks in and out of the tank)
Oh, and welcome to the forum! :)