LaTeX, 9766 bytes
\documentclass[tikz,border=9]{standalone}\begin{document}\tikz\draw circle[radius=1];\enddocument
\input tikz\def\f#1{~\vfill\centering\tikz\draw circle(#1);\vfill}
I consider the "canvas" required by this challenge to be the default text area of a latex page. The code defines a macro \f that takes the radius in cm as an argument.
Example Code
\documentclass{article}
\input tikz\def\f#1{~\vfill\centering\tikz\draw circle(#1);\vfill}
\begin{document}
\f{3}
\enddocument
Outputs a PDF:
