I think from the strictly legal point of view you're OK (but of course, I'm just an ordinary person, not a legal expert). Do you have any idea if the Passport Canada employee spoke Spanish? I can see why some people from certain Spanish speaking countries would say that Velez shouldn't be a middle name.
Of course, the right course of action here regardless of any of my speculations is to follow Senorita Bella's advice and call CIC/Passport Canada just to make sure.
There this problem in Quebec is that they don't understand middle names in the same way as the rest of the country. If you declare a name as a middle name in Quebec, it won't show up in any document other than a birth certificate. If you want it to show up, you must declare it as part of your first name, and then it will show up absolutely everywhere. There is no middle ground.