Realistically IMHO - Schedule III would be used for 2 things:
1) when someone gets in trouble for possessing with intent to distribute "without a license." We have the same thing here in the states. It's a way for them to slap the rest of those charges on those unfortunate souls that get caught.
2) if that day comes that MDMA can be prescribed in some manner, this is a precursor to ease that transition without changing the schedule class on it. - this one is coming from my mind, don't take it as gospel.
BTW- check the rest of the Schedule III list in Canada:
* Amphetamines (Adderall, Adderall XR, Vyvanse, Dexedrine, Dexedrine XR, Mixed amphetamine Salts) (Excluding Methamphetamine)
* 3,4-methylenedioxymethamphetamine(MDMA)
* 2,5-Dimethoxy-4-methylamphetamine (STP / DOM)
* Cathinone
* DET
* DMT
* Flunitrazepam (Rohypnol)
* GHB
* Harmaline
* LSD, but not LSA [1]
* Mescaline, but not Peyote (lophophora)
* Methcathinone
* Methaqualone (Quaaludes)
* Mecloqualone
* Methylphenidate (Ritalin, Focalin, Focalin XR)
* Psilocin
* Psilocybin
* Some Barbiturates (barbiturate hypnotics indicated for short-term treatment of insomnia that are intermediate acting [half-life range of 8–48 hours], include: pentobarbital, secobarbital, and amobarbital).