Welcome to the Community. We appreciate having users like you post in questions for others to chime in on.
At this time, QuickBooks Online doesn't have the capability to produce T5 forms. I recommend reaching out to where you're required to provide that info and ask what's the best place you can get that from. If you feel this feature is critical to you and your business, I encourage you to send feedback about this to our engineers. You can do this by clicking the gear icon and looking for Feedback. Product ideas and improvements are mostly based on the great feedback we get from users like you.