Where the custodian resides really becomes most relevant in a default situation, when things go wrong.
If the private keys reside with a domestic regulated trust company, for example, asset holders can rest assured that the windup of the custodian will follow a predictable course of action as established under Canadian laws. Also, if the custodian is a trust company, the client has certainty that the legal title to the assets remains with the client and will therefore be returned to the client as part of any default proceedings. With international custodians, given that other regulations and legal proceedings would be in play, there's an inherent and unavoidable level of extraterritorial risk.