as much as I like making everything n one piece: I would knit seperately here and sew. Suzee is right: you will not work comfortably around the corner and it will not only be effort, but also pull on your knitting and the pick up edge will not really look nicer than the sewing. Since you see both sides of the seam here, I might consider to do a "stitch over" /visible stitches running over both pieces, or one of the types of crocheting together - just for a neat look.
Continental Knitter with passion, pretty busy and always onto something new.
I have been away from the forum for a bit, but I am still around!