For your sleds that say non-transferable, did you have a loan at all when you first got them? If you did then you need to show proof that the loan has been paid I think to get a transferable registration. Just like a clean title for a car when you sell it.
For your friend, I think it’s not gonna be easy. I made the same mistake but mine was entering Canada with my jeep without filing paperwork. I could not register it in Quebec. They wanted me to return to the USA with it. Then file paperwork to export to Canada and then cross it back in. Nightmare.
Finally I got lucky and got hooked up with a customs officer at the port of Trois Riveres. I brought jeep there he looked it over. Just checked VIN number and my title and he filled out necessary papers I needed to go register it here in Quebec.
I got lucky.
Your friend may have to cross into Canada then come back to USA side and declare he is importing sled bought in Canada. Probably pay duty and any other fees and show All paperwork from dealer he bought it from.