Do not reheat this drink if you've added protein powder! I'm not sure about all protein powders, but mine, when microwaved is not pleasant.
I use Presidents Choice Natural Source Whey Protein Isolate, the unflavored and unsweetened version. I have not experimented with any other protein powders or with using a sweetened version, but just be sure that it's one that you don't mind the flavor of on it's own before trying :)