As a Canadian returning home from a day the USA we normally are asked 4 ? They are - where do you live, how long were you out of the country, how much did you purchase, any alcohol or tobacco. If all are answered politely then we get a "have a nice day" and we go home. This is the exact process that occurred the last 3 times, it's almost like it's a script or something like that.
As a Canadian leaving home for a day in the USA we are usually asked a lot more ? Some of the more usual ones are - where are you going, how long are you staying, carrying any fruits or vegetables, are you leaving anything in the states, are you carrying $10,000 or more. If you are going to stay a bit in the states then ? about where you will be staying ( eg. Motel etc) is usually asked. Again speaking politely is the best and short answers are the best bet to get through with very little hassle. However, if the border person himself decides to open up the conversation then we have found that almost all have a quick wit and a pleasure to talk with. My wife and I are nature photographers and if we say that when asked "where are you going" and we say to look for some birds we have found us having many great conversations with the said guard, much to the displeasure of the long line of cars waiting behind us. One must remember that these people have a difficult and stressful job to do. Their main job is to protect the country and its people as best they can from harm brought in by others ( even their own citizens)! Probably a job I would not like myself.
My wife and I cross back and forth over the Canada/USA countless times (probably 40-50) every year with little or no problems as long as we remain polite and civil with the border personnel regardless or the direction we are travelling. Just be ready with your papers (passport) and answer all ? clearly and civilly and you should have no problems. But for God's sake don't tell an untruth for if caught the results can be disastrous. I know some people who crossed the border at one area (such as Detroit) and then recrossed the border elsewhere (such as Sault Ste Marie) have lied about how long they were out-of-country so as to bring back more purchases duty free. That now is a no-no as the border computer systems for each country are now tied together so that a passport scanned by the US authorities will be shown by the Canadian computer scan when you try to recross. They always know exactly how long you we're across (even though that is one of the ? asked 😱). If you do be ready for a good fine and future border crossing problems.
Another untruth that is fairly common is for those south of the border, this one dealing with firearms. Handguns/firearms of any type are severely banned in Canada but still a considerable number of people will falsely claim to have none even though they do when crossing into Canada. If the border guard is suspicious that a unclaimed firearm is present he can do an extensive search himself, or if too busy can give the information to the Federal Police Force (RCMP) to do a follow up check. This means the person could be stopped much later at a distance from the border and then have a extensive search done. Either way, if a undeclared firearm is found it will result in confiscation, large fine and banned from crossing in the future. Not something any traveller would aim for, all the result of one "little"lie. Since I personally do not own a firearm at the present I don't know the consequences of bringing one into the USA, maybe similar!
So if you are planning coming into Canada/USA and also returning play it smart and don't rock the boat, tis not worth it.

LittleRed (Ron)