In Canada, the Banking Act RSC 1991, c.46 regulates most banks (except for provincially-created credit unions and caisses populaires.) There are two sections that deal with unclaimed balances: s. 438 (for domestic banks) and s. 557 (for foreign banks).
From the Bank of Canada's unclaimed balances site:
When there has been no owner activity in relation to the balance for a
period of ten years, and the owner cannot be contacted by the
institution holding it, the balance is turned over to the Bank of
Canada, which acts as custodian on behalf of the owner. Balances are
transferred to the Bank of Canada once a year, on 31 December.
The Bank of Canada holds unclaimed balances of less than $1,000 for 30
years, once they have been inactive for ten years at the financial
institutions. Balances of $1,000 or more will be held for 100 years
once they are transferred to the Bank of Canada.
If the balance remains unclaimed until the end of the prescribed
custody period, the Bank of Canada will transfer the funds to the
Receiver General for Canada.
The original bank is required to send a notice to the account holder on January of the 2nd, 5th, and 9th years after the account has gone dormant (ss. 439(1), 558(1)), and interest is accrued until the account is transferred to the Bank of Canada (ss. 438(1), 557(1)). After the 30 or 100 years (depending on the amount) are up, the federal government receives the money and it goes into general revenue.
Credit unions are different, as provincial legislation affects them. For example, in Alberta the Credit Union Act RSA 2000, c. C-32, s. 117, requires credit unions to notify the account holder after 12 months and 2 years, after which the money goes into the credit union's unclaimed money account (s. 117(2)). If the amount is less than $100, after 5 years the credit union can claim the money (s. 118(5)); otherwise, after 20 years the provincial government receives the money and it goes into general revenue (s. 120(6)). Other provinces will have similar provisions.