Pierre writes, "I went to the United States by car, drove all over the country, and was having such a good time that I even forgot to return for a while. It seems that I overstayed but when I went back the Canadian agent asked me a few questions and waved me through. I do not have any stamps in my passport by either country and I was never clear how long was I allowed to stay. I know I was there like 7-8 months. Do you think I have a ban now? Will I have trouble going back to the US?"
Legally speaking Canadian citizens entering the US are allowed to stay up to six months in a 12-month period. While no I-94 is issued or the passport stamped, there is a record in the databases when you arrived and left (you only go through Canadian immigration while entering Canada and US immigration when entering the US and the two countries share the data), so that serves as a record of your stay. The bans for overstaying are imposed manually (you would have been told so when you left the US) and are not automatic (not assigned by a software). Most likely you do not have a ban but expect some aggressive questioning (probability is low that it would happen but it might depending on the mood of the agent and how soon you visit after your exit) because if the officer suspects that you maybe trying to settle down permanently or work without authorization or engage in some other unlawful activity, you may have to explain that. As long as you explain what you were doing for 8 months the last time (having some evidence of your travel will help) and describe what you plan to do in this visit, you will be allowed back in (particularly if you have proof of employment and strong ties to Canada). If there is a ban already or if you are denied entry due to a ban imposed at that time, you can apply USCIS Form I-192 for advance permission to enter as a non-immigrant but you should do so with the help of a law firm.