Your original post, in the Gap Year RTW forum, indicates that you are interested in two months of driving around the US and Canada. But a more recent post indicates you may drop the US from your list because of the cost and other factors such as a high drop off fee for leaving a rental car in another country. As a proud American, I want you to see our country. So here are some possible options for you to consider.
Instead of getting a car, get a camper. Be aware the savings in hotel bills may be offset by the higher fuel costs. But buying groceries and cooking would be cheaper than restaurant meals. Since you are traveling such a great distance, you need to be concerned about the fuel economy of whatever vehicle you get. Google Maps may help you plan your trip. But this website will also calculate estimated fuel costs for different types of vehicles and several alternate routes: https://www.viamichelin.com/ .
Instead of driving down the Pacific coast, inland to national parks, then back to the west coast to fly out of LA, why not keep going from the parks back to Toronto? That would not be a substantially greater distance than backtracking, and would allow you see more of the US. Make a big loop from Toronto west to Vancouver, south to LA, and east to Toronto via the parks.
Instead of renting a car, perhaps lease a car. A two month lease may be cheaper than an eight week rental. I have not done it in Canada, but it's worth investigating.
You might also consider buying a vehicle, and reselling it at the end of the trip. It's possible you could pre-arrange a buy back with the person selling it. Insurance for a vehicle you own may be substantially cheaper than a daily fee to a rental company. Obviously, there is a risk you might not be able to sell the vehicle at the end of the trip, but there are also various risks in renting. It may also allow you more flexibility with a vehicle you own, free of rental car restrictions. Of course, if you have pre-arranged the sale at the end, you need to honor the agreement. Again, I have not done it, but it's worth investigating.
Perhaps consider flying into the US and driving to Canada, rather than flying into Canada and driving to the US. Detroit, Cleveland, and Buffalo are the closest US airports to Toronto, and even closer to Hamilton. If there is a substantial savings in airfare and car costs, it may be worth it. You could also check Seattle, and start your Canadian trip in Vancouver, driving east instead of west. My guess is airfare to Seattle would be higher for you, but maybe not.
Have you considered buying a RTW airline ticket, rather than a series of individual tickets? Here is an old post with some options:
https://www.lonelyplanet.com/thorntree/forums/gap-year-round-the-world-travel/topics/rtw-travel-agent?page=1