I think the Canadian Tire trailers probably
are the equivalent to the Harbor Freight and Red Trailers. A friend of mine had a very tiny one which he started to build into a camping setup.
SnowBear trailers are sold at Costco, among other places. One difference between these and the bolt-together kits is that these are made of box-section tubing, welded together. They don't come in very small sizes, and tend to come with utility sides. The ones I have seen at Costco have a complete checkerplate steel floor (although the ones on the web site do not).
The SnowBear trailers (again, as sold at Costco) do not need the sides for structure. The sides are on posts which go into stake pockets on the sides of the frame, and the ends are removable as well. The axle has forward (nearly central) and rearward (more typical of teardrops) mounting locations. I think they would be a decent base, if you could buy one without the cost of the unnecessary utility sides.
Here in Alberta there are dozens of companies which will build a trailer any size and type you want; Allandale is just one example.
These cargo trailers have springs and axles intended for significant loads. I can't see building a teardrop which would need even stiffer springs. I
can see wanting brakes, and the small cargo trailers are usually kept to 2000 lb GVWR or less to dodge the legal requirement for brakes, which they don't have. That's an advantage of getting one built - you can choose the
right springs, hubs, brakes, wheels, tires, and dimensions, not what suits the average cargo trailer buyer.
