The prices when I looked weren't that different- it was about C$30k Canadian for air source and C$40k for ground source (which I went with).
40K is also on the low end for geothermal. I'm guessing you were able to trench instead of drill?
If you can afford ground source it's by far the best option in cold climates. Steady ground heat means you get the same efficiency all year round. The install can be eye-watering though.