If you stay more than 31 days the 8840 form needs to be filled in every June. The consequences of not doing so can be quite dramatic.
As of June 30, 2014, the border crossings automatically share the dates when you cross from one country to the other. The result is that Canadians may stay only 120 days in USA per calendar year.
FULLTIMEWANABE wrote:
If you are spending a large amount of time down in the USA then you should also look into whether/when necessary for you completing Form 8840 based on your previous 3 years presence = closer connection to home form courtesy of Uncle Sam.