Canadian-listed ETFs that trade in US securities can be subject to some currency risk in addition to market risk, meaning the ETF is exposed to movements in the value of a currency as well as movements in the value of the stock held in a portfolio. Certain Harvest ETFs offer Class A units which use currency forwards to hedge their value to the Canadian dollar, limiting currency risk.
Class B units are un-hedged. You can learn more about currency hedged ETFs here.
Class U units trade and pay their distributions in US dollars. This class is useful for investors who want to receive their income in US dollars. You can learn about class U ETF units here.