  We present surface photometry of a giant, low surface brightness stellar arc
in the halo of the nearby spiral galaxy M63 (NGC 5055) that is consistent with
being a part of a stellar stream resulting from the disruption of a dwarf
satellite galaxy. Using the stream's "great-circle" morphology and its
photometric properties, we estimate that the stream originates from the
accretion of a 10^8 M_sun satellite in the last few Gyr. The B-R color of the
stream's stars is consistent with Local Group dwarfs and is also similar to the
outer regions of M63's disk and stellar halo within our measurement
uncertainties. Additionally, we identify several other low surface brightness
features that may be related to the galaxy's complex spiral structure or may be
tidal debris associated with the disruption of the galaxy's outer stellar disk
as a result of the accretion event. Using our deep, panoramic optical view of
M63 with additional existing multiwavelength data, we describe the possible
effects of such an accretion event in the larger picture of the parent galaxy.
