Legally Register Any Car

We do not have titles per se, however we now use a transfer of ownership document from seller. Tax is due on the book valuation or the purchase price on the document, whichever is higher.
I went through this method when I brought a car across the border. I had all the proper customs forms filled out, and the registration, so there wasn't any issues since Canada (British Columbia is where the car was registered) doesn't have titles like most states have.