The smallest Wii disc image is the infamous Wii Backup Disc, at 10,485,760 bytes in WBFS format (of course including the update partition) - you could have about 23000 copies of that after estimating filesystem overhead

Of course it's not a game (and in fact doesn't work fine as a backup at least on base 36 CIOS), so next up is Mario All-Stars (230,686,720 B) - conveniently about 1000 copies (again, a lot more if you remove updates)

The european version of Brawl, the largest Wii title, is 7,654,604,800 B - 33 copies of it!

Actually, many music games are a lot larger if you include all DLC (theoretically possible with emunand), but I can't comment on that