When I had to answer a similar question in which I had visits too frequent to list each one, I instead gave a table with "type of visit" (for example, shopping trip), "frequency" (for example once a week), "duration of trip" (for example 6 hours), and period (for example, March 2010 to present).
In my situation it was how many times I had visited Canada on my provincial nominee questionnaire. Having lived in Michigan, where you can go to Sarnia to buy an ice cream cone at the dairy, or go to Windsor to go curling, also lots of shopping trips when the exchange rate was quite different than it is now, there was no other way to answer that question. I never got questionned further on that point, so it was sufficient for me.
When I did the citizenship test, they asked me how many times I had been out of Canada, and I told her twice a year to the U.S. for about 10-14 days each trip plus one additional trip to the U.S. or Mexico per year for a week, depending on where my husband's conference was that year. They were well aware that the Canadian and American customs people don't often stamp the passport, so they didn't even look through them, and were satisfied by my verbal statement. They did want photocopies of the passports, but they didn't look at them at all. I got a sense that trips to the U.S. barely even count against you... In addition, I'm not sure that a visit which isn't overnight would even count... I should add that I had been permanent resident for nearly 6 years at that point so residency wasn't close to being an issue.
