The Canada Border Services Agency says its officers made the discovery last Tuesday.
According to a CBSA news release, a suspicious box caught the attention of border service officers who determined that it had been tampered with.
There were backpacks inside the box, which contained solid packets that tested positive for heroin.
The CBSA says the seized heroin has an estimated street value of $8.8 million.
So far this year, CBSA officers working in the Greater Toronto Area have seized more than 106 kilograms of suspected heroin from the region’s airports, postal and cargo processing facilities.
Goran Vragovic, a CBSA regional director general, said the most recent seizure was an indication of "the vigilance and expertise of our officers at our ports of entry."