Cool tolerant Ficus, here I mean might keep growing vigorously even when temperatures dip as low as 15 C (about 60 F), these should do better in a average Toronto home or apartment without a heat mat. Ficus don't totally stop growing in cooler weather, but most will switch from vigorous growth to fairly slow growth. Repotting and pruning during cool weather is not recommended.
Ficus microcarpa and any of the Taiwanese ficus seem more temperate than F religiosa
Ficus natalensis - Natal Fig, wide distribution in northeast South Africa, seems to tolerate cooler weather, (not cold, just a little cooler)
Ficus sp, 'Chiapas' similar to the willow leaf fig, but different, from Chiapas, Mexico, also known as Ficus sp. 'Mexicali' distributed by Jerry Mieslik, it was collected in city of San Cristobal, state of Chiapas, Mexico, This one grows vigorously even when a bit cool, a dip into the 50's F, (+10's C) won't stop vigorous growth, though prolonged cool below 15 C will slow growth to the semi-dormant speed.
Ficus sp, Willow leaf fig as distributed by Weigert's Nursery in Florida. The origin (Jim Smith) and name of this species is unclear, it is often call F. salicifolia or F. nerifolia, but in the first case it clearly is not the African species F. salicifolia, and its provenance does not trace back to Africa, and the species F. nerifolia is poorly defined. Don't know what species it is really, but it is great for bonsai. It may in reality be a Neotropical species. Seems to grow well even when somewhat cool.
Ficus carica - Culinary, or Mediterranean fig, the fig you find in the grocery store - leaves are large, the internodes can be long, it is a coarse shrub with no fine branching, but there are some dwarf cultivars, a good one for the ''Eat your Bonsai'' collection if you find a dwarf cultivar. Most cultivars are USDA zone 7 hardy, some a little more hardy. They grow rapidly during the short warm summers, and will keep growing as cooler weather sets in.
Ficus aurea & citrifolia - the ''Florida'' strangler fig, both species can be found in Florida. Leaves tend to be about 4 inches, but can reduce. Native to Central America, and into Florida.
Ficus pumila - Creeping fig, this is a thin stem vine, but it is very cold tolerant. I've seen it growing on fences and walls in Memphis, USDA zone 7, a delightful small leaved Ficus. It takes forever to develop a trunk, you must force it to get bushy, then let all the branches grow out many feet. It is possible to create trunks over 3 cm in diameter, which combined with the small leaves can make a nice shohin. I believe Bruce (
@Shima ) has one with a trunk over 7 cm, maybe as much as 10 cm in diameter. Worth a try as a long term project. It will take years to develop a trunk.