To my minde comes R. moyesii.
It is by far my biggest self supporing Rose. In the 8 years it grows in my garden it grew about 3m tall and the biggest stem is roughly 6cm at the base. It also does not tend make many new canes from the base but is willingly branching on older wood. So with bit of pruning somthing “tree like” might be obtained.
What about RosaXspethiana ('Spek’s Improved) and Rosa roxburgii? Cross these with canina and you have a giant.
Moyesii: 'R. moyesii' Rose Photo
Longicuspis var. sinowilsonii : prefers heat, but is thirsty, and mine is self supporting 'R. sinowilsonii' Rose Photo When matched with shrub form hybrid musks it will form relatively well behave large self-supporting shrubs like my sinwilsonii hybrid that is sinowilsonii x ‘Violette’. ‘Violette’ is not a shrub-form by any stretch but I used it because of its rep. of making ‘Sweet Chariot’ and I’ve been very happy with this initial result. This shrub, this year, has reached about 10ft tall: 'SV-2011-RLSxV' Rose Photo
I also feel gigantea might be persuaded to contribute to tree-form. I am attempting to grow mine as a shrub… if the wildlife would leave it alone…
I was just remarking to myself that my Ross Rambler #4 is growing in a way that would make a good tree. Strong vertical shoots have horizontal side branches. Not much suckering so far.