Well firstly, if you are still in saudi, it is comparitively easy... (comparitively in terms of everything in Saudi)... you need to get a form from your local Police station for PCC, then get it attested by MOFA and Chamber of commerce. Now these two agencies dont entertain people like us, so you need to ask your employer to help you... and as you know, the employers will not be happy to hear that you have a Canadian visa procedure in progress... so better start finding alternatives...
http://workinginsaudiarabia.blogspot.in/2012/07/procedure-for-police-clearance-i n-saudi. html