Ironically I came here in Aug 2009 also to be with my gf. We were then married in October.
I've been here for 8 months, and I've been back to the States twice for less than a week. My delima has been that since I do not have a work permit I do not have legal status to work. I've been waiting five months for the FBI clearance which was reject once, just so that we can apply for Permanent Residence. At this point I have another 6-8 months (or more waiting) for legal status.
If I may ask what are your marriage plans?
Also how often have you crossed the boarder in say the past couple of years? If you have made regular visits, have you ever had any trouble coming here to Canada?
If you cross the boarder by car, my guess is they rarely stamp your passport. In my case in traveling across the boarder it has always been in her vehicle which has Ontario plates. (I don't know if that factors in since I was not bringing my car.)
As it has been said IO is interested that you have legal status to be here (in Canada). Since you do not need a visitor visa, you can stay legally for six months. The second thing is that you are not planning to stay indefinitely without legal status. That is why they ask about job, where you live (City and State) family and how long you are staying. I would only bring what you need for a reasonable vacation. And that you are visiting your gf. I've found that humors them. As they ask how long you've known each other, and how often you see each other. I would not make anything up as you do not want to be contradicting yourself.