We bought our Castita in North Dakota and towed it bad to Alberta. We had all the emails regarding the purchase and pictures of the serial plate when we crossed the border. We bought a temporary license
sticker for it in North Dakota. Crossing the border we had to pay the GST on the purchase price less the amount that you can claim for the time spent in the US. Our trailer was over 15 years old we did not have to have an inspection or do the RIV program fees. The border folks will ask for any communication between you and the the seller so print out those emails(to prove the purchase price, not something you dreamed up for tax purposes). If it newer than 15 years you need to do a RIV inspection and I think its around $200 for the paperwork.
We could not find out if the temp license
was valid in Canada so just towed it home and pleaded innocence
In ND you can even buy a temp license from a state trooper but we went to a license office. I think it was about 35 for a 2 month permit, which was just stuck in the back window of the trailer.