The picture below shows a detail of cutting your canary's toenails - as long as they are fine-tipped enough to be accurate, you can use any size of scissors or clippers. I use these larger ones because I find the extra-fine tip allows for better accuracy, while the size makes for easy handling.
Never cut more than 1/3rd of the entire length of any toenail, no matter how over-grown. You should be working in a strong light, so that you can make sure that you can see where the end of the quick inside the nail is before you cut - if you snip this, you will have to deal with blood!
Dark nails make this next to impossible, but as long as you keep to the 1/3rd rule mentioned above you should be okay. Keep a small cup of plain white flour nearby when cutting nails - should you accidentally cut too far down the nail, use this and a little pressure to stop the bleeding and encourage clotting.
Personally, I don't like to use styptic pencil to stop bleeding - it stings, and the birds protest and wriggle...
Most canaries are quite calm throughout the nail-clipping process, if held correctly - they can breathe easily, and can grasp one of your fingers with one foot, while you are working on the other, one toe at a time.
I call this fine fellow Major Minor - he is named for the way he sings.
How To Cut Your Canary's Nails