I've read multiple sites and forums that sand perches aren't good for canaries because the rough surface would injure their little feet--they're not as thick as the bigger birds.
The last time I had to clip Peeps' nails, I had someone holding him so I got to focus on clipping them. We made sure to do it in a well it area so I could see his vains. I got the nail clipper for small pets from Amazon, it seemed to do the job well.
Personally, I don't feel comfortable grabbing Peeps though. So I'm also considering taking him to the vet instead since they provide the service. However, I don't want to put him through the stress of travel and strangers grabbing him either... I think I'll have to practice lol