On the back of my Cub is a plate that is bolted to the draw bar. This plate is bolted in 2 of the holes in the center of the bar and has 2 outside holes. Originally it had a 3" ball in one hole and a 1 7/8" ball. I changed the 3" ball to a 2" ball.
If you change the attachment of the wagon to connect with a ball hitch your Cub should pull it easily. I attached my 1963 Mallard travel trailer to the 2" ball[in the center]. I can pull the trailer all around the property with my 1968 Cub Lo Boy. The trailer is much heaver than that wagon. It has a full birch interior, a table with 2 seats, a stove and furnace, 2 beds in a bunk set up and upper and lower cabinets. It has propane interior lighting, stove and furnace. I have it stocked with stuff to go camping. Your Cub should pull the trailer easily.
If you decide NOT to change the hitch to a ball or another type of hitch; use the method the other guy suggested and split the tube so you have an upper and lower flange. I have a low red trailer that you can find on line and in other farm stores that has an upper and lower flange. I put a pull pin in the hitch in a hole two spots off the plate with the ball hitches, on the draw bar. I use the pin and a cotter key in the lower pin hole which secures the pin and the hitch. I have hauled a lot of the smaller sections of wood [in my thread] with the red trailer. There are all types and sizes of pull pins available and cotter keys to secure it. I have a pull pin and key on the back of the Ford Edge that secures the reese hitch. I have a similar orange trailer at my house where I used to live. [I live with my mother and am her 24/7 caregiver....this is not my house where the other trailer is] This trailer I used the pull pin and cotter key that I currently use on the Edge with a 300 series John Deer riding lawn tractor. I hauled a lot of wood and things around my home uptown. I think if you can effectively use the trailer and the cost suits you …..it will work any way you decide to fasten it.
A side note to the draw bar. Since the plate with the hitches is on my draw bar bolted in place; I have had the need to "roll" my lawn this year several times. The roller tongue has a rusted pin in the hole as the draw peg. I drop the pin/peg on either side of the plate 2 holes over giving it room to swing. I have rolled the almost 2 acres of property here with the offset roller and the Cub Lo Boy. The Cubs are stiff tractors and can haul a lot. I have drug 2 larger logs with chains as well as large piles of branches with 3 chains all together pulled by the Cub [documented on my thread]. You should be fine with whatever you do.
Richard