I live on the Canadian prairies too. Here's what I've found helpful:
- get an energy audit from the hydro company, the kind where they do the blower-door test. This will give your house an eco rating and they will tell you what you can do to improve it. They might also offer a grant for some kinds of work, like insulation and new windows.
- triple pane, gas-filled windows make a big difference in both heating and cooling.
- basement insulation is a priority over attic insulation if you can only do one at a time. If you're doing the basement yourself, use 2 x 6s.
- well-fitting doors and of course storm doors and good weather-stripping are important.
- ceiling fans help a lot with both cooling in summer and pushing heat down in winter.
- large shade trees around the house help a lot. Deciduous on the south, conifers on the north.
- bungalows with basements are better that 1 1/2 or 2 story houses.
- larger lots keep houses cooler in summer, due to more air space and less material to heat up.
- yes, south-facing windows are good. Also, avoid north facing windows and especially, doors.
- an attached garage is better for temperature regulation than a detached one.
- a high-efficiency furnace is more cost effective than a mid or low-efficiency.
- lastly, beware of making your house TOO airtight, or you may have humidity problems. When I had my eco-audit done, the hydro guy said my house was amazingly airtight, and said I should think about a HRV unit. I decided against it, since the door gets opened enough times in a day to avoid any problems.