The collapsing of multiple spaces is a browser feature and has nothing to do with SugarCube. Regardless, you're probably going to want to use something like the following to get your ASCII art to display as you'd expect (<nowiki> for SugarCube, <pre> for the browser):
<nowiki><pre>
your ASCII art here
</pre></nowiki>
NOTE: Using the above within the bounds of one of the no-break features could still cause issues, so don't do that.