In an embodiment, the invention relates to the seeds, plants, and plant parts of canola variety SCV406503 and to methods for producing a canola plant produced by crossing canola variety SCV406503 with itself or with another canola variety. The invention also relates to methods for producing a canola plant containing in its genetic material one or more transgenes and to the transgenic canola plants and plant parts produced by those methods. This invention also relates to canola varieties or breeding lines and plant parts derived from canola variety SCV406503, to methods for producing other canola varieties, lines or plant parts derived from canola variety SCV406503 and to the canola plants, varieties, and their parts derived from use of those methods. The invention further relates to hybrid canola seeds, plants and plant parts produced by crossing the variety SCV406503 with another canola variety.