Personally, I don't think it would be good idea to keep Corys and Guppys together. If I am not wrong, I believe Guppys do better with harder water.(If I remember correctly, doesn't people keep with little salt?) Anyway, I thought they do better with alkaline side of water. And I know most of Corys if not all prefer acid side of water.
I guess you can take the middle ground of netural water, but this means you compromise for both fish. Rather than that, probably better if you keep fish with similar preference.
Anyway, that is my 2cents. And I hope you'll consider the water prameter before put the fish together in the tank as well as the compatiablity.