importing quebec to ontario

There's no real "import" when you are buying from Quebec to Ontario. If you are buying from a dealership in Quebec, you'll likely have to pay the taxes there, you'll pay them again in Ontario and then apply for a refund from QC which can take a good 6 months (this might have changed but that's how it was when I did it many years ago). You'll have to do the regular Ontario Safety Certificate and Emission test when you get to Ontario. The only tricky situation is if the car has a QC rebuilt title. I that case, I believe you will need to have a structural inspection done in Ontario which can be a pain because many garages won't do it because they say it's too much of a headache (normally, when doing structural inspection, you need to provide documentation listing all part replaced / repaired - you won't have that as it's a re-inspection but the garages I've asked about it says that it's a pain dealing with Ministry of Transport and they won't do re-inspections because of that).

As far as driving the car, I'm pretty sure the used car dealer I bought from provided a QC temporary plate. If you are buying privately, contact QC DMV / Ministry of Transport and find out what you need to do to get a temporary permit. You won't be able to get an Ontario one until you transfer the vehicle to your name (i.e. have the signed over ownership) so probably won't be able to use an Ontario temporary plate unless you do 2 trips or buy it sight-unseen and the owner sends you the signed ownership.