First, let me just say congratulations to you and your partner! I'm a bit surprised and upset that it's been difficult to find a Humanist wedding commissioner in Manitoba. This is something that we should really look into in the future.
Unfortunately, past the Unitarian link that Brian posted, I don't know of anything or anyone in Canada that can help.
One of the issues is that Canada requires religious non-profit organizations to include worship a deity. At least, that is according to Spiritual Humanists (
http://www.spiritualhumanism.org/ ). It would be very nice, however, if it were recognized in Canada, as anyone can become an ordained Spiritual Humanist minister for free. Who better to perform the ceremony than someone that you already know and trust? I'm not sure what is involved in getting weddings performed in the US recognized in Canada, but if having the ceremony down in North Dakota is an option, then
anyone you want could perform the ceremony.
Edit: Check out
http://www.spiritualhumanism.org/directory.htm and go to the Canada section. There are some people that note that they can perform weddings there, though none are from Winnipeg. However, you can try emailing them to see if they know of anyone in Winnipeg who could perform the ceremony, or if they're willing to travel (while keeping costs reasonable of course...)