I don't think there's any "inbuilt" number line in Canvas, but you can just add an image of one (either getting one online, or making it in an image editor).
One application is (if you have access to New Quizzes) to use a Hot Spot question to have students click on a region of the image that represent the numbers within a certain inequality.
Alternatively, a somewhat basic one can be added as HTML (note no CSS is allowed in the rich content editor on Canvas). Here's one option (to be pasted in the HTML editor in the rich content editor to guarantee the right spacing):
<pre>
0 1 2 3 4 5 6 7 8 9 10 →
┼───┼───┼───┼───┼───┼───┼───┼───┼───┼───┼
</pre>