Currency conversion apps change the 'display price' of your products based on the customers location. However, they do not change the actual checkout currency that you have configured in your settings. Your customers will need to check out in your CAD currency, these apps are useful because it will give them an accurate price on how much the product will cost them in their native currency once their bank converts the funds.
With that said, since you are using Shopify Payments you can actually configure it to sell in multiple currencies. We have a guide here explaining how you can get that setup.
If there is anything else I can help you with, please let me know.