What is the ruling on opening a bank account with a very small interest rate (0.15%) in US dollars in Canada, knowing that it is the only option to avoid significant loss when transferring expenses, and it is not possible to keep the money in cash?

If you need to open an account in USD to avoid losing money when converting it from Saudi Riyals, there is no harm in that, even if the bank charges a commission for the transfer and gives interest on the money held with it. You can take the interest and dispose of it by giving it to the poor and needy, or benefit from it yourself if you are poor.