I used EXIF-tool and it recorded my Sigma lens correctly but it doesn't show the correct (full) lens in Lightroom, so I think it's more of a Lightroom issue.
There are two separate metadata sections in a photo that record lens information, the industry-standard EXIF section and the manufacturer's proprietary MakerNotes section. They usually store different information about lenses.
As explained above, both Exiftool and LR's Lens Corrections panel use Canon's MakerNotes:LensType field (a simple number) to look up the full name of the lens in their own lens databases.
Whereas LR's Metadata > Default and Metadata > EXIF panels display the lens information that the manufacturer (Canon) records in the EXIF metadata section of the photo. Canon is not recording the full name of the lens in the EXIF metadata section or in the MakerNotes section for that photo.
To see precisely what's recorded in the different metadata sections, use the "-a -G -n" options with Exiftool:
exiftool -a -G -n photo
That will demonstrate that Canon is not recording the full lens name in the EXIF metadata section and just a number for MakerNotes:LensType.
Note that when Exiftool displays MakerNotes:LensType without the -n option, it automatically translates the number stored in the file to the corresponding full name stored in its database.
As I stated above, it would be better if LR displayed in the Metadata panel the full lens information shown in the Lens Corrections panel.