I have had good luck with "James Bryddon" and "Pink Sensation" in my pond. I actually planted both varieties in the pond bottom and not had them naturalize to other areas of the pond. Pink Sensation is heavily scented and smells terrific. My advice is to call Slocum Water Gardens or Lilypons and ask one of their experts about the suitability for zone 5.
I have tried a lot of different waterlilies, including many tropical varieties. If you decide to grow a tropical water lily variety you need to surround the tub with some chicken wire or other protection or muskrats will clean them out. You can remove the protection once the plant gets larger. Apparently tropicals taste really great. I live at my pond so landscaping the part near my house is very appealing. I have had one variety of hardy hybrid get out of control and I had to kill it all. I am pretty sure this was "Caroline Strawn" a pretty pink lily but very aggressive.

Layton Runkle