for at least 12yrs I drove Toronto to Orlando. to visit parents in florida as well as to go to Disney with kids or whoever wanted to tag along. straight down I 75 best time of all was camping in Fort wilderness in Disney world its a rather top notch campground no line up to get into park. kids, grandkids even today say it was the best time.

Hi there!! Thanks for sharing! I'm planning a 3-4 day drive down I 75..any opinions?i know that it might sound like a crawl but umm Singapore( where we are from) has the right hand drive system instead of the left..and although it is not our first time driving in the U.S., I was hoping to arrange the trip in a way whereby we wouldn't have to spend one whole day in the car..so is there any stops to recommend or any opinions about the timeline? Thanks a bunch..

"If you drove to Montreal and did not tell the rental car company they would be very unlikely to find out unless you managed to get a traffic ticket while outside Ontario. "
Think again. Do you know what year this is ? Many rental cars in 2015 have hidden GPS trackers that broadcast their location by SMS text messages periodically over cellular connections. These now cost under $20 and are installed in hidden locations such as under the dashboard by mechanics who remove the console or dashboard for access. They are wired into the car's electrical supply and so don't need batteries.
Because I heard some car companies place tracking devices on their car and hence they would be able to know where we've been and stuff..
True.
There are Wikipedia pages that explain GPS tracking and vehicle tracking in particular.
The rental car company can track your vehicle in real time. There are web based and mobile apps that connect to the monitoring server to which these units broadcast their locations that show your current location on the map and can make a path of all the places you have been.
When you return your rental car the company has a complete record of GPS locations for your car.
"Maybe the sat-nav that they are charging a ridiculous rental fee for is also telling them that you have left Ontario."
Very wrong. The tracking devices many companies use have nothing to do with sat-nav. As can be seen from the above link they are small, contain a GPS chip and a cellular GPRS data transmitter, are now around $20, and can easily be hidden inside interior surfaces by mechanics. If a company uses these devices they will be present regardless of whether the auto renter rents a sat-nav.
"Ok..thanks marka55! We would be using our own navigator though!"
Please don't reward misinformed and very bad advice,

hope you have driving in ice / snow exp. as winter storms quite possible that time of year, to encounter until you reach southern US states. myself was rear ended by tractor trailer rig in ohio. van totaled which is how I ended up driving a uhaul truck.
Just as another bit of reassurance, I fly regularly to Manitoba and always hire a car for a up to 10 days or so, while there.
I've driven to Vancouver and back and gone the other way too, Halifax and return. Literally 1000's of kms. and never paid an extra cent. Couldn't comment on Enterprise though, as I've never used it. However, while out there, I've used numerous co's.
Have a great time !

I'm surprised no one has commented on the timing of your trip. In December, you may well find yourself driving in snow going or coming back. There is no guarantee at that time of year that the weather will not affect your travel plans. You can find yourself half way from Toronto to Florida (or on the return) and not comfortable with the driving conditions.
As someone familiar with driving your route, I would try to avoid planning a driving trip in December. Most people would FLY from Toronto to Florida and then fly back whether stopping in Washington and New York or not.
A road trip from Toronto down to Florida Orlando then back up to New York, Washington then lastly leaving Toronto.
I think 400 km per day is plenty - I would never plan to drive more than that (on any given day usually, let alone as an overall trip average) - we think a good North American road-trip average should be about 250 km per day.
Definitely take your own GPS with USA-Canada maps in it - they are too expensive to rent. Definitely check for any damage (however little) on the vehicle when you pick it up - and mark it all down on the booking form.
Definitely do not take the vehicle out of Ontario / into the US if it is not permitted ... simply do not do it. If Enterprise cannot allow that, use another provider. We use carhire3000.com to book vehicles overseas - never had a problem with them. We never take the 'extra extra' insurance cover - we risk the $900 excess on the CDW (or whatever the amount) if there is a collision.
And yes - you may strike bad road conditions north of Washington DC / New York City. Where will you stay in both those cites with a vehicle, by the way?

#16 Ian, there is no problem with taking the vehicle to the US, the only issue is that if you remain in Ontario then the rental is unlimited but if you drive outside Ontario then the 400 km per day limit applies to the whole rental.
Okay - that's clearer (odd indeed - but presumably there to restrict those wishing to do a fast cross-country run ).
So anyway ... if they travel sensibly then 400 km should be more than enough over the full rental to Orlando and back.

Here is a 2016 update.
We rented a intermediate SUV (Toyota Rav 4) SUV for a summer vacations from Enterprize. Unlimited Mileage, No Geographic Restrictions for $723 plus tax. We booked in February. Now it's May and I was considering changing the date by one day. The new rental price is $1417. Needless to say, we kept the original booking date.
So the lesson is always book about six months in advance for a summer rental and you will save a lot. We also booked from the costco.com site instead of the .ca site. Prices for both sites were in Canadian Dollars. But they always seems to give the American Costco customers a slightly better deal. You need to be a Costco member, but with savings like this, it will pay for the membership many times over.
I find that every year, the company with unlimited mileage - no geographic restrictions change. Also i'm sure it changes depending on the area of the country you are renting from, so you need to shop around. I'm sure one of the car companies will have the deal in your area.