VANGUARD gathered the suspects were arrested on Sunday at a guesthouse in Phnom Penh's Meanchey district after they had smuggled the drug into the Cambodian capital from Laos.
"Police seized more than 20 kg of the drug, which was packed in 21 plastic bags," the National Police said on its website.
"The trio are being questioned and will be sent to the court for legal action in accordance with the law."
The Southeast Asian country has no death sentence for illicit drug traffickers. Under its law, anyone found guilty of trafficking more than 80 grams of illicit drug will be jailed for life.
According to an Interior Ministry report last week, the authorities had arrested 8,750 drug-related suspects, including 167 foreigners in seven nationalities, in the first six months of 2019, and confiscated a total of 343 kg of illicit drugs.