This is a debate that has been going on forever. No matter the financial institution you deal with (PayPal, big bank, etc.,) there is going to be a difference in what you are offered for an exchange and what the "posted" rate is. I have found that typically the big banks offer a rate that is about .5% better than what PayPal offers. This is just due to the volume that the big banks deal in compared to what PayPal deals in.
We opened up an RBC Centura account. You need to file forms with the IRS, (your bank helps you with this), but as mentioned earlier, you are not American, and you are doing business in the U.S., so you aren't giving any money to the IRS.
We opened up the US account in order to make our $US purchases. With a $US credit card, you keep you money in the same currency. You are saving between 4-5% of your money by doing this.
For example, let's say that for the purpose of this scenario, the Canadian dollar is on par to the US dollar. You make a sale and take a $100 payment in US dollars.
If you were to take that $100 in US dollars and make a stock purchase of $100 in US dollars, you don't lose any money, so the $100 you collect gives you $100 to purchase.
Now take that same $100 in US currency that is in your PayPal account. You convert that to Canadian dollars and deposit it to your Canadian bank account. You now have about $97.50 Canadian.
Now you take your Canadian dollar credit card and make a $100 purchase in US dollars. Your credit card company will charge you about 2%, which means that your $100 US purchase will cost you about $102. You only have $97.50 in your account, so this transaction cost you about $4.
Bottom line is whenever possible, avoid currency exchange, it doesn't matter who is doing it for you, it is going to cost you money.
If you are collecting revenue and $US and making purchases, or incurring expenses in $US dollars, then avoid the exchange whenever possible and open up an account in the US. Most big banks in Canada have subsidiaries in the US, so it is easy to do.
Just my thoughts.
Peter