I considered John Johnston -- whose son was named after DH Cooper -- having read that he lived along the Canadian before the war. Cooper definitely would have known the name was Johnston and not Johnson. It seems unlikely that the transcriber would have consistently transcribed Johnston as Johnson since the letter "t" is usually easy to recognize. For these reasons I thought him unlikely.
I imagine Canadian Depot/Camp Johnson/Johnson's Place/Johnson Depot was located just south of present Eufaula. Cooper says it is "south of the South Canadian". I assume he is referring to the main Canadian River and not the South Fork of the Canadian though it would be close to both. I assume it to be at the junction of the Texas Road and the road from Ft Smith south-southwest of North Fork Town.
I haven't had time to dig into this more but if memory serves me, this is where Cooper was camped during the 2nd Battle of Cabin Creek and where Watie came after the battle.
To add to the confusion, it appears in later reports (later meaning after January 1863) that Steele refers to Johnson's Station on Brushy Creek on the Butterfield Route (Ft Smith-Boggy Depot Road) as "Johnson's Depot". Of course, both were supply depots at times.
There was a civilian commisarry agent named C.B Johnson -- I believe this is Charles B. Johnson that Pike refers to in one of his long ranting reports. I don't know anything about this person but I wonder if there is a connection between this person and Johnson's Depot, Johnson's Station or both.