If either the American or or Canadian police find drugs in your car they will assume it's yours
Possession is 9/10ths of the law. If there are drugs in your car a border agent will assume it's yours. Do not ask the American police to screen the car for you. They'll think you're a drug mule checking your work. If they find drugs they will assume they are yours.
You can file a police report if you want. They will probably show up after 3 hours, write a report and walk away. They will not check anything.
At the very least go to a self-service cleaning lot and do a thorough search of your car and vacuum everything. Personally, I'd go to a full-service car wash and pay for a deep interior cleaning just to get rid of the ick factor.
Many drug runners steal a car at night - use it to run pounds of drugs, then abandon it before the owner wakes up. I know this because one of my friend's had her car stolen likely for this purpose. The cops found it that afternoon and told her they suspected this happened. The cops didn't do a search of the car.
I'd suggest a professional deep-clean + a thorough check yourself of any nook or cranny you can get to without tools.
EDIT - in response to this answer. Which is dangerously wrong.
There is also a saying - tell it to the judge. People will insist they are innocent and someone hid drugs/guns/money in their car, house, or on their person to frame them regardless of mountains of evidence that suggest otherwise.
I'd bet the first words out of every mule's mouth are "those drugs aren't mine."
Think about it - if you could get a get-out-of-jail free card by having the cops check your car before-hand, then you'd get them to check - THEN put the drugs in.
If you ask the cops to search your car and they find something, they'll just assume you are a dumb criminal, and book you anyway.
If the cops on either side find something they'll book you, tell you they don't care about your story, and to explain everything to the judge. The judge has probably heard this before too.