You can choose to sell less of the asset but you can also quite simply buy up massive amounts of reserves in a different currency. The CAD's value relative to t

You can choose to sell less of the asset but you can also quite simply buy up massive amounts of reserves in a different currency. The CAD's value relative to the USD was motivated by the need to buy CAD in order to purchase the oil. This can be offset by using the royalties, and more, to buy up USD-denominated assets to balance the demand and lower the relative value of the CAD. As an example, there is a reason that the Chinese government his such a prolific purchaser of US treasuries, and it is not because they are particularly bullish on the US.