jQuery try to match each attribute name with a jQuery function name. Matched functions are called.
width and height are jQuery functions, so your original code is equivalent to this:
var newCanvas =
$('<canvas/>',{'class':'radHuh'})
.width(100)
.height(100);
width(value) and height(value) functions set CSS width and height of an element.
Relevant jQuery source code line (https://github.com/jquery/jquery/blob/master/src/attributes.js#L308)
if ( pass && name in jQuery.attrFn ) {
attrFn object definition (https://github.com/jquery/jquery/blob/master/src/attributes.js#L288):
attrFn: {
val: true,
css: true,
html: true,
text: true,
data: true,
width: true,
height: true,
offset: true
},