Best if you ask Hertz, not Google users.
Hertz will need to weigh in. Over the years, I've rented many cars that I have driven into Canada (or the other way around). When I've driven one-way rentals (from Canada to the US) I have always informed Hertz what I was doing. Usually, they end up giving me a car that they want to have back in the States. This, I believe, is because they are actually two separate companies with separate assets that they prefer to keep straight. I never had to pay extra, but that may have been because of the corporate rate I used -- which may not apply for you.
Thanks for the replies. My mistake as l thought the question was going to Hertz
I agree with Thelonious, contact Hertz directly as well as your personal car insurance company if you plan on using your personal car insurance on the rental.
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