Working with sales tax when it comes to cross-border transactions can be tricky, so I'm glad you're looking into this and verifying the details you need before moving forward with this transaction. I'm here to help ensure you have the information you need for not only charging the sales tax, but also for accurately recording the transaction in QuickBooks Online.
For this kind of question, I like to direct QuickBooks users to the Canada Revenue Agency. While QuickBooks is an accounting software, knowing how to handle things from an accounting perspective can still mean checking in with sources like the CRA to ensure there are no mistakes you'll have to take care of later.
The CRA has a number of great pages about charging sales tax as a Canadian business owner and there's also a tax tips line that you can take advantage of for these kinds of situations. Here are some links that may help you.
Those should get you started, but I also encourage you to check out the CRA website in more depth if these pages don't answer your questions.
In the event you'd like to work with an accountant, QuickBooks Online's My Accountant tab is designed to keep things simple. The tab gives you the opportunity to invite someone you're already working with as a user to your account so they can help you directly in your books. There's also the Find a pro to help button to research our database of QuickBooks-certified accountants near you.
I hope this has been helpful for you! Feel free to stop by the QuickBooks Community again if you have further questions. :)