With that said, as of this writing, the Canadian dollar is trading at 0.7459 USD. Let us use a 2016 Honda Civic as an example. In Canada the MSRP on a 2016 Honda Civic is $15,990 CAD, while the US MSRP is $18,640 USD. First off, without taking the exchange rate into account, you can save almost $3,000 alone in Canada but when factoring in the current exchange rate, a new Civic in Canada is under $12,000 USD! Simple math tells us that this is a savings of over $6,600 (that's almost a third of the price gone!). Keep in mind that the Canadian dollar at one point this year was trading under $0.70 USD so potential savings could be even higher (or lower depending on how the Loonie fluctuates).
Now for another example; let us look at the cheapest car in Canada, the Nissan Micra. The base model Nissan Micra has a manufacturer's suggested retail price of $9,998 CAD. And when converted over to US dollars, that works out to just over $7,400. Americans right now can purchase a brand new car for under $8,000 although, to be fair, it would be lacking in some creature comforts such as power windows...
In terms of actually purchasing a vehicle, you can go at it alone or hire an auto brokerage firm. VSI Worldwide Trading, for example, specializes in sending new vehicles from Canada and the United States to Europe, Asia, Australia, and South America. You would have to find a broker that ships from Canada to the United States and some additional brokerage fee but they will also help you shipping from a port city and with the paperwork.
If you choose to purchase a vehicle yourself, you'll need to get a few ducks in a row. You'll need to contact the U.S. Customs and Border Patrol if you are shipping a vehicle down to the States or if you plan on driving the vehicle down to the US from Canada. Additionally, you should also contact the Department of Transportation as well as the Environmental Protection Agency to ensure the vehicle you purchase meets safety and emission standards (sorry, I don't think the Micra will meet these standards). Taxes in Canada range from 5% in Alberta to 15% in Nova Scotia, so remember to factor that into your price. Duty is another cost one needs to take into account although, from my research, most vehicles made in the US and Canada are not subject to duty.
Again I would like to reiterate that I have no knowledge of American import laws, however I have heard and read about Americans purchasing a vehicle (along with other items) in Canada and bringing them back to the States. Please check any relevant laws before considering purchasing a vehicle in another country and for an accurate value of the Canadian dollar, check the Bank of Canada's website (www.bankofcanada.ca).