One striking similarity between both is that they both represent the notion of a bildungsroman set against the ever changing social conditions of the time period. Franklin's narrative is a part of the changing colonial culture, a moment in history when the new nation began to articulate its own voice, which in part led to the America Revolution. A narrative like Franklin's is a part of this change. The same can be said for Douglass, although nowhere near the relative comfort of Franklin's. Douglass' work depicts the changing face of culture in America regarding its treatment of the issue of slavery. This particular instant is one that would threaten to divide up America, learning to the Civil War. A major difference between them would be that Franklin's narrative voice serves to represent the promise and possibility in the new world, while Douglass represents the harsh reality and denial of opportunity, which was sadly also present in the real world.
I'm not trying to compare/contrast the plot etc, just the use of literary elements.