I went to each company's site to check on taking a rental car into Canada from the United States.
Although I could find no information for Thrifty about taking one of their rentals from the U.S. to Canada, a look at other company policies were as follows:
Note: There are always the possibility of location exceptions to this policy. Make sure to check local policy when making reservations. You can often find a link online when searching for car rental rates (often at the end of a rate quote, before actually booking)... usually called local policy, terms of rental, location specific details, etc. Any exceptions that I find, I will list below:
Alamo
According to Alamo.com you may take an Alamo rental car into Canada, with the permission of the renting location and as long as the vehicle is returned back to the United States.
Avis.com (opens in a new window) states that as long as there is advanced notice and permission from the Avis location, certain cars may be rented from the United States and into Canada by U.S. residents. A Canadian non-resident insurance card may be required and is available at the Avis rental location.
According to Budget.com
(opens in a new window) a U.S resident may drive a Budget car into Canada as long as you advise the Budget location upon vehicle pickup that you plan to drive to Canada so that a Canadian Non-Resident Insurance Card can be placed in the vehicle.
Exception: Vehicles rented at Salt Lake City, UT locations may not travel into Canada, Connecticut, Maine, Massachusetts, Mexico, New Hampshire, New York, Rhode Island, and Vermont.
According to Dollar.com (opens in a new window) at most Dollar car rental locations driving is permitted into Canada. Renters must refer to the local policies, which are found within the reservation process, for location specific information and policies regarding travel into Canada, for the location from which you wish to rent.
Some Enterprise locations will allow their vehicles to cross international boundaries. Renters should contact the specific Enterprise location that they plan to rent from to see if they allow their vehicles to cross into another country. You can find local office phone numbers at Enterprise.com (opens in a new window)
From most locations, rentersmay not take a rental car into Canada. Exception: Cars rented at the SEA location may be driven into Canada... you must recieve authorization from the rental location.
*Fox cars rented in Florida, must stay within Florida.
According to Hertz.com a renter will need to inform the rental counter if they intend take the rental car into Canada, in order to determine if this is allowed by that specific location.
If a Canadian resident wishes to rent a U.S. car in the U.S. and drives into Canada, the renter must obtain a Traveler's Vehicle Permit from Canadian Customs, Form E50B. The renter must go directly to a Canadian Hertz location once over the US/Canada Border and exchange the U.S. car for a Canadian car within 24 hours. (No one way rental fees will be applied in this situation.)
Renters must have a valid license and rental record. Rentals from some cities may require presentation of Liability Protection Letters, Certificates or Stickers at Customs for driving into Canada. These items will be provided by the Enterprise location.
According to Nationalcar.com a U.S. Citizen renting a vehicle in the U.S. may drive across the U.S./Canadian border with no restrictions. The driver may be asked to show a rental agreement and a form of identification, such as a driver's license and/or passport at Customs, before taking the rental car into Canada.
According to PaylessCar.com, (opens in a new window) geographic restrictions may apply and are location specific. In order to determine if a renter is permitted to take a rental car into Canada, you must check the "Location Policies" (during the reservation process - bottom of the page on step 3 of the reservation process, before booking) to determine what geographic restrictions may apply for rentals from the specific location you will be renting the car from.
Rental Car into Canada for non-US, Non-Canadian Citizen
Most of the US Car rental companies provide general policies with the assumption that the renter is a US or Canadian Citizen. It's difficult to determine policy that may be different depending on a different country of residency.
In order to determine the border crossing policy from the US to Canada for a different country of residence, you would need to make sure to enter that information before checking availability and pricing.
On most car rental websites there is a section at the beginning of the reservation checking process that allows you to input your country of residence. Once you do that, continue to checking a potential reservation )(ie inputing city of pickup and return, dates and times, car type, etc) and then making sure to look for any possible link during the rate quote process that lists local terms, local policy, terms of rental, terms and conditions, etc. This is where you will find any information on whether or not travel into Canada will not be allowed with the rental vehicle from that particular location and or company.
If the car rental company's website does not offer the option to specify your country of residence, and/or a link to location specific terms and conditions for the rental, you would need to contact the car rental company directly (ie by calling their toll-free reservation line) in order to determine if the car rental company (location specifically) would honor your request as a non US citizen to take their rental car into Canada.
*Note: Car rental companies can modify policy at any time; I make every attempt to maintain up-to-date info, but always check with an individual company to verify any policy. See: Disclaimer
Note: Border Crossing Policies provided on Car Rental websites generally cover only US or Canadian residents. Residents of other countries should contact their specific rental pickup location to get permission to take the rental car across the border.