Thank you and your response is along the lines of what Canva support advised me: "As long as you incorporate the stock media on a design by adding elements, photos, texts, videos, or backgrounds, you can comply with the One Design Use License Agreement and are free to do the following: ...print design on products for selling."

Since I lack design skills I opted to buy commercial licenses for ready-made designs. So I guess if you have some design skills Canva is a good option as you mentioned in your post.