Another Torontonian here. We purchased our trailer from CanAm RV in London.
Reasons we went with a dealer were that I wanted my car properly set up for towing (Andrew from CanAm is an expert) and that I wanted to buy a trailer with as few surprises as possible.
We ended up choosing a 1984 34' International. Bigger than we had initially planned, but we've got three young kids and the space is welcome.
When we bought the trailer it had been serviced from end to end. Everything that needed fixing had been fixed, it had been re-sealed and checked for water damage. The a-frame had been stripped and repainted, all rust spots had been fixed, a new power jack and a new toilet had been installed. The batteries were new and the propane tanks were full.
Our trailer had been a CanAm towing demonstration unit and came with a Hensley hitch ready installed. When I picked the trailer up I stayed overnight at the dealership, plugged in, to test all systems. The next day I got a three hour introduction to towing and backing up on a nearby empty lot.
We opted to have additional work done; a bunk fitted in the kid's bedroom, all upholstery changed and modernized, new flooring and the gaucho remodelled so it now folds out into a full queen bed.
All work was done at a very competitive price. Next fall we'll have the interior refinished and a composting toilet installed.
The price we paid was about 20% more than what comparable trailers were advertised at from private sellers, but we chose to pay that premium for peace of mind.