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):
{{Old AfD multi}} (1st and subsequent nominations, preferred template)·{{Multidel}} (2nd+ nom)·{{Afd-merge from}} (merge contents into AfD'ed article)·{{ArticleHistory}} (AfD, Good/Featured, and many other article "events")