Wealthsimple has 170 billion in assets under administration, while BMO, the smallest major bank, only has 310 billion. Considering WS is 100% retail, it's arguably a major financial institution at this point (though legally not a bank).
Isn't it legally a bank? It provides chequing and savings accounts (registered and unregistered), and it's even CDIC-backed on at least their managed products.
Wealthsimple is best known for their robo product, not their banking. It's the Canadian equivalent of Wealthfront.