This is wildly, wildly, situational based on "du jour" market requirements of that rental agency.
As you might guess, demand for rental cars changes regionally throughout the year, and rental agencies often must re-position their cars. For instance, Vail Colorado uses a lot more cars during ski season than the rest of the year. Repositioning costs them money – they must pay 4 drivers to move 3 cars (the 4th car brings all back), or hire haulaway companies.
When they price one-way bookings, they account for that. If your one-way trip relieves them of the need to pay someone to reposition that car, you will get a favorable price. However if your one-way means they will have yet another car they’ll need to reposition, the one-way fee will reflect the costs of doing so, and they may even turn your business down flat if they just don’t have the capacity.
Of course, it is axiomatic that most people want to move in the direction most people want to move! So most of the time that one-way fee will be quite bad.
Yes, I’ve done exactly that (with Hertz) a couple of years ago. Wasn’t more expensive than usual.
Is it possible to rent a car in the US, and return it in Canada?
Yes e.g. https://www.budget.com/en/help/usa-faqs/cross-into-canada:
Based on availability at each location, one-way rentals to Canada may be allowed. In order to check the availability of such rentals, renters should fill in an online reservation form and set their preferred pickup and drop-off locations.
Credit:stackoverflow.com‘