This template should be subst:'d and takes two parameters, the second one being optional:
To specify a specific canvassed editor:
{{subst:canvassed|1=Username|2=(optional)link to diff (resembling http://en.wikipedia.org/w/index.php?diff=prev&oldid=12345)}}
To specify the generic "editors", make |1= blank:
{{subst:canvassed|1=|2=(optional)link to diff (resembling http://en.wikipedia.org/w/index.php?diff=prev&oldid=12345)}} or:
{{subst:canvassed| |2=(optional)link to diff (resembling http://en.wikipedia.org/w/index.php?diff=prev&oldid=12345)}}
This template supports up to 8 diffs (parameters |2= through |9=), mostly for the "editors" rather than particular username case (e.g. to identify notifications to select wikiprojects with a similar viewpoint but no particular stake in the matter, or a number of editors notified at their user talk pages):