For retail customers (not using a corporate flat rate one-way mileage charge plan), there likely won't be a separate "drop fee," but a higher daily rate, often much higher for a one-way between different countries. Whereas one-ways within the US average about $85/day plus tax for an economy car, between the US and Canada can come close to $200/day plus tax.

The reason is that whereas a car from, say, FL can be sold at, say, the south Jersey auto auction when its time in the rental fleet is up, a car from Canada was built to different specs, and so can not easily be sold and registered in the US. And vice versa. So demand needs to be controlled somehow, and a sure way to do that is with a high price.

One-ways to border cities can take a car with Canadian plates, since the car will likely be one-wayed back to Canada at some point. But one-ways deep inside the US almost always have a restriction that the car must have US plates. Which state of registration won't matter, between corporate stores. Ex, Someone on the National forum was given a car with Michigan plates in Toronto to return to Boston. But this restriction is because the car is highly unlikely to get another one-way to Canada.

What I would recommend is try to get a National Emerald Club free day, or 1,200 Hertz Gold points, for a free one-way day. (Since this is the Hertz forum, please visit the National forum to learn more about the National option.) It will allow you to pick up in Toronto and return to NYC, with unlimited mi/km, for free.

You said you are a party of 6. Minivans are apparently not bookable for this one-way. So you would need 2 drivers renting 2 cars, each of appropriate size to hold any associated luggage.

Also, let's assume you can't get free days, and have to pay $250-300 for one day with each car, plus gas and tolls. That's not a good value. But it might still be cheaper than airfare, Amtrak, or bus for 6 people. Only you can decide whether price or value is more important.