You're not the only one who does this. I have the same for every bike, trailer, car, everything I've sold. There's a video of it driving away along with time stamped photos of the bill of sale, cash/payment, etc. If **** goes down, I'm CYA.
Here's the one from my old VTX on the new owners trailer trailer ready to head out. Took video of it going down the road.
View attachment 67275
Man, I miss that bike. Shoulda kept it. Many memories.
You can do it immediately after you sell it, you don't need to wait and see if the seller changed it into his/her name, you can go and file a report that you sold it and it'll be removed from your name at that moment. When I last did this it was a little form I needed to fill out so yeah, you needed to do so in person. I wrote about this here at the time, it was an eye opening event when I went in to buy a new licence plate sticker about 6-8 years ago and they asked me for "which motorcycle". Except I only owned 1 bike, or so I thought. Turned out I still "owned" a bike I'd actually sold in 1995 as well as it had never been switched. Also found a camper I sold in 1998 or so, a horse trailer I sold in 2018 or something like that, and I think a utility trailer as well. Point being, you can ask to see what vehicles still show in your name at a service ontario, and perhaps you might be surprised as well if you have sold stuff in the past that the previous owner may never have changed to avoid paying the taxes. I filled out a form for every one of them and had them removed from my name immediately. I've done the same for every vehicle I've sold since, sometimes within an hour of selling it.
As for the plate, you won't get anything back for it anymore like the old days of licence plate sticker refunds, so IMHO...keep it and hang it up on a wall in your garage/basement/whatever as a memento. If at some point years from now you buy something with 2 or 3 wheels again (who knows), you can always reuse it then again and save the new plate fee at that point as well.