20s are small for suvs. 20s with low pros are tiny! I think that would be like 3"-5" smaller than the stock tire (depending on how low-profile you go). IMO you would need atleast 26s to achieve a 20s with low pro "look" on an suv like the h3.
Here is a site that helped me visualize what different tire sizes and rim sizes would look like compared to stock.
tirecalc
Good luck, and keep us updated!