The grow-ops were side-by-side on Murray St., and featured "sophisticated ventilation and watering equipment, transformers, lights" and more, Brantford police said in a news release.
In the first semi-detached house, police found 371 marijuana plants and more than 7,000 grams of weed that was ready to sell.
The second home had even more marijuana, including 1,709 plants — worth over $1.7 million, according to police estimates.
Brantford police called it a "significant seizure" and said "not since 2010 has there been a seizure of this magnitude in our community."
In that 2010 bust, the street crimes unit seized over 2,600 pot plants.
Two men were arrested in connection with the grow-ops.
One, a 62-year-old man from Brantford, faces three charges including production of a controlled substance and possession with the purpose of trafficking, as well as breach of probation.
The other man, 34, is from North York. He was also charged with production and possession with the purpose of trafficking.