How do I seal a vapor barrier on my basement walls if I have none from the floor above?
Vapor barriers tend to be one of the most hotly debated topics in home building. I redid a basement in MN a few years ago and ultimately went with Building Science Corporation's recommendation which would apply to your climate as well. See this answer for details: https://diy.stackexchange.com/a/8644/1209

Summary: Do not use a vapor barrier. Instead use EPS or XPS foam for your insulation which will act as a vapor retarder, but not trap moisture like a barrier would.