volunteer what?

In the plot that had cucumbers last year, this large-leaved seedling has sprung up.

At first I thought it was a cucumber plant, but then I found two identical seedlings on the side of driveway. No way cuke seeds got over there. But a sunflower seed could have been dropped by a bird. So I looked more closely at a photo of young sunflower last year, and am pretty sure now that's what this is.

I'm tempted to dig it up and move into a better spot, but after reading Thalassa Cruso's dismaying incident with sunflowers, not sure that's a good idea. (She left volunteer sunflowers alone, and the following generation was crazy-tall plants with small flowers that fell over constantly making a mess.)