Not sure how it is in Ontario, but in Manitoba this is what I do:
I just recently purchased a 96 2 months ago, and paid the 5% gst at the border, but your not obliged to pay provincial tax until you register it. I just keep the X under ownership but do not register it......when spring rolls around and want to drive it, I will get a 30 day temporary insurance which is about $170/month for about 7 months of driving before winter hits again. I will continue pay this for each month. This may sound a little crazy, but here are my reasons:
1. You don't have to pay tax on what you paid, in my case it would of been about $2100.
2. I don't get any photo radar tickets...ie red light camera or mobile units. which usually saves me at least 1 ticket a year......a value of about $200 and up for each ticket.
I don't usually keep cars for long periods of time, therefor coughing up the 7% tax to me seems wasteful.