Leafly lists 6,822 cannabis strains. Though 'strains' or more aptly cultivars are often not reflective of the actual underlying chemical nature of the plant [source]. They are ultimately not very meaningful in general.

Based on this database, Europe has 104 varieties of hemp registered.

Canada has 87 but there is probably overlap.

Though potatoes and cannabis aren't really a fair comparison for many reasons. There are a lot of different species of potatoes with major chromosomal differences but cannabis only has 3 species.