NickB488,
I respectfully disagree. The fastest route Toronto-Sarnia-Calgary (per Google maps) is 3,421 km and 33 hrs. Going north through Sault Ste Marie and then the UP is 3,248 km and 33 hrs. The roads are not faster if you factor in 2 border crossings and the delay around Chicago. Besides, there's currently an awful lot of construction on the 94 that can cause substantial delays. And if you took 2 you also have two lane roads for a substantial section, a little shorter, but according to Google, more time. (I know that Google times are approximate. For my own calculations, I usually add a third.)
I maintain my position that the exchange rate will eat up whatever savings you might assume due to lower gas, meals and accommodation prices. We just came back from a lengthy stateside stay, and the exchange rate was substantial, even when getting cash at my local bank. If you use credit card, there's the 2.5% exchange rate charge on top of your purchase on almost all credit cards, after the exchange was made.
To the OP, you would also need a passport, or if you live in Ontario, an Enhanced Drivers Licence, to cross the border.