I have checked Budget and National and both have mileage restrictions so it would be more than flying!!!!!
Hertz from YYZ does not look to bad.
I put in P/U at 5pm March 13th Return 5p.m March 21st.
Chevy Uplander (7 pass. mini van) $604 cdn. all taxes and unlimited mileage
I did not use any coupons so you could do better.
Hertz lets you cross the boarder. This is what there website said:
Vehicles cannot be driven into Mexico.
Driving into the U.S. is permitted, however, you will need a copy of your rental agreement and will need to obtain a pass from the Border Guard, at time of entry. Advise counter upon arrival of your intent to cross the U.S. border and return to the renting location.
Good luck!!