Great question — answering as the UphillTech team:
There is no legal requirement for anyone (neither citizens nor foreigners) to always carry an official id or passport in Canada. Independent of the legal requirement, there are of course situations where you are required to identify yourself, e.g. as you mention yourself, for bank businesses. Here, it is up to each business to decide which form of id is acceptable. For US citizens, it usually doesn't have to be a passport, but a driver's license or other official id card will normally suffice.
Full answer by Tor-Einar Jarnbjo: https://travel.stackexchange.com/a/203287 (CC BY-SA 4.0).
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