+1(514) 937-9445 or Toll-free (Canada & US) +1 (888) 947-9445
Factors they consider:
1) Eligibility - do you meet the minimum required experience within the prescription period (including language requirement)
2) Admissibility
a) Criminality - have you been convicted/involved in certain criminal activities
b) Medical/Health - do you have condition(s) that will be a burden to the Health and/or Social services
c) Security - do you pose a threat to national security

People get denied if they or their accompanying dependent(s) do not pass at least one of these
 
The CEC program is one of the best programs available right now. It is a pass or fail scheme. That means either you are qualified or you are not.

They have a quota, you can check here:
http://www.cic.gc.ca/english/immigrate/cec/applications-accepted.asp