Just a quick update.
The first time my husband crossed the border (by land) he had to go inside. Actually they make all occupants of the vehicle go inside. You have to turn off your vehicle, they put a bar behind the tire so you cannot reverse and you have to hand over your keys. They brought out agents to escort us in while someone else parked our car. They asked if we had any weapons and had to keep our hands out of our pockets. I'm sure the car behind us thought we were criminals

They issue an I94 form which is valid for 6 months that they staple inside the passport. It cost $6.00US payable by credit card or US cash. On your last trip before the 6 months is up you have to turn that paper into Canadian Immigration when you exit the US (so you have to figure out when your last trip will be) and then you would have to get a new one the next time you cross.
We went on a Saturday and crossed at Queenston/Lewiston (Ontario) and it was very busy!!!!! I asked if then when we crossed we would just be able to go across. The agent said yes but.....when we crossed a week later on the way to the airport we had to go in again. Although I think it was because my husband, a little nervous with the questions was anticipating one question and got another one. The agent asked if he had ever had trouble at the border before and he thought he was going to ask if he had crossed before so he said yes. I tried to just explain it that we had crossed the week before and had to go inside for the form. I figured that was time for someone to do a further check on the computer as his next question was if my husband had ever been arrested before. I thought that might be the last of it but no. I crossed 5 days later in the same vehicle at the same bridge with my daughter (both cdn citizens) and we had to go inside again! So I'm not sure if they have flagged the vehicle or what.
So just a note to give yourself extra time for crossing the border if you do have the visa. The next time we visit my family we will try crossing from Ontario into Michigan to see what happens
My husband had a 10 year U.S. visitor's visa up until he got his Canadian passport a few months ago and now he no longer needs the visa… yaaaaahhhh!!
Anyway, we travelled to the U.S. several times by car (crossing at both the Niagara Falls, NY crossing and the Gananoque, Ont./Watertown, NY crossing). We always had to go through the customs booth and then pull over and go inside to fill in the I94 form to say where we were going and how long we would be there (not me because I am Canadian but my husband had to do this). They stapled that little I94 form in his passport (Dominican passport) and stamped his passport with a U.S. entry stamp. The little paper was good for him to come and go for six months. However, we always handed it back in on our return trip to the customs agent (did not have to get out of car and go in – just hand it to them at the little kiosk) because we never knew if we would be back to the U.S. within six months and we never wanted to worry about not having handed it in if we did not return within that timeframe.
The fact that they did not ask your husband to go in and get the I94 form on some trips seems very strange because the whole point of the I94 form is to make sure that all visitor’s leave the country so everyone needs to get one and then hand it back in within the six month visitor’s entry allowance. My husband and I were always very diligent about making sure we gave the little form back when we returned to Canada so that the next time we wanted to visit the U.S., they would not question whether he overstayed his visit allowance on a previous trip.
I am sorry to hear of all the problems you had in dealing with the U.S. customs agents because we never ever experienced anything like that. We just pulled up our car to the designated parking area, got out, left our car unattended, no guards, nothing stopping our car tires, etc. Thank God… that would not have been a nice experience. Once inside the little office inside, we just waited in line and filled out the form. My husband had to answer some questions and that was it… on our way.
The one time we flew to the U.S., we filled out the form at Pearson Airport in Toronto and they just asked him some simple questions, stamped the form in his passport and waived him through. The U.S. customs office for U.S. bound flights is right there at Pearson so we did this before we even got on the plane and then we did not have to go through any customs when we landed.
As for you getting pulled over when you aren’t even with your husband, perhaps they have tagged your licence plates and sorry to say but maybe they think you might be smuggling people or something into the U.S. because I can’t think of any other reason they would pull you over on your way in. It also sounds like you cross the border often though so that could be another red flag that has triggered them to check you when you cross.