Police say the fire broke out shortly before 12 p.m. on Mackle Road near Cavendish Boulevard.
Officers found a marijuana grow-op inside one of the apartment units.
The two tenants — a 29-year-old man and a 56-year-old woman — are being questioned by police.
Residents were treated on the scene but no one was seriously injured.
The police's arson squad is trying to determine the cause of the fire.