FWIW: This worked for us to get the facts: Simply google FORM 8840 and you will get all the info from the ultimate source easily. Keep a copy of it with you when crossing back and forth into the USA. Also keep a copy of your tax return, couple of utility bills, property taxes, maybe bank statement or two. This can prove to the officials you are able to support yourself without working in the USA and you have close ties to Canada to return.
Gbopp: Only if you reciprocate and do the same to pay for our government employees here!