I know nothing about Canadians time limits etc for coming to the USA. You probably want to look more like a vacationer or snowbird rather than just a person crossing in a vehicle with no plan. Just my guess.
It's not like there are crazy people running around killing people everywhere in the USA. To me it's all about where you are at. There are areas of most any city that I wouldn't go. I wont go to areas of Yuma at night yet it seems like a pretty decent place in the day time and same for Lake City Florida. It's all about risk and people. You could stop in a rest area along I75 headed south and have a higher chance of getting robbed or having your vehicle broke into because you have a more mixed crowd traveling that route. On I75 north through northern Mich you are more likely to run into people like you or I who live up there or vacationing. At the same time we also had locals in northern Mich who were following older folks home from the drug store and mugging them. Rare but stuff happens anywhere. They are just far more likely to get shot in the USA.
On one hand if someone plopped you down in the middle of Detroit in my opinion if you were walking you would be lucky to make it out alive and certainly just about absolutely be mugged.
If you weren't at least mugged then it would probably be because they think you are crazy and something was up. Now if they plopped you down in the state forest off the side of M72 near Grayling it's going to be a very long walk to Mc Donalds. You may have someone pull up and ask if you are ok or need a ride and the state police would probably pull up and ask you what's up.
Speaking of Michigan and probably may cities I can tell you that if you plan on stealth parking on the street or in city park parking lots etc it may not work out well. There are ordinances in most areas as far as sleeping in your vehicle. Some people do become good at it and make it work.
If you are planning on camping and traveling the USA you can do it and pretty cheaply. It obviously works better in some states than others with most of it being more to the west.
As you go north in Mich and the state lands and national forests start you can disperse camp on thousands of acres. The Michigan DNR website has a one page permit that you fill out and you can disperse camp after following their guidelines. I suppose someone could rip you if they saw your stuff out there but it's unlikely. The most vulnerable areas are closer to the populations. The areas where a couple local yokals randomly hit you. I have been to hiking trail heads in a few areas and noticed crushed glass in the parking area. Well....to me that's from the locals seeing you go in there knowing that you will be out on that trail for a while and they smash a window for your valuables and split. It's situational in that respect and probably happens in Canada too. There are even places out in the sticks that we size up and dont feel comfortable in so we move on.
Yes, most people are ok so you need to position yourself with those people. Where I'm camped we dont have a problem with anyone stealing anything. I have a problem with people leaving gifts at our steps when we are gone and I rack my brain trying to figure out who it was. I have worked on peoples rv's that we met along the way and would stop in a heart beat to help one out. I consider everyone from the tent dweller to the big MH people to all be in the same group. Yes, even those truck campers ;). Many of us who boondock will sort of touch base with each other and have some continuity and watch out for each other.
If you have the financial means it's a great place to follow the seasons and live pretty cheap. You can develop friends and I will tell you that there are fantastic people who will teach you the tricks. Free camping, free water, free dump sites and all the best deals.
You are here so you are already among friends.