Hi, I had the same problem and ended up leaving it blank. Actually based on what I've checked it only let's you fill it in is if you choose Canada as your country of residence. So I guess that it is not intended for tourist visits.
Just make sure you mention your visit on the Declaration where you write your travel history.
I still don't have any news from CIC so I'm not sure that I filled it in properly, but the only other option was to write it by hand once you print out the form. And I thought that might be a bigger problem.
Hope this helps!