what are is the main difference b/w certificate program and pg diploma??

[PAVAN24]

I'm from mechanical stream i want to study further in Canada.Due to some reasons i'm having more no.of backlogs (including attempts 16) what are my chances of getting visa.Many of my friends told that with more no.of backlogs i'm having less chances of getting visa for pg diploma.So i'm planning for certificate programs.what is the main difference b/w certificate programs in universities and pg diploma.which one is better to do MS after completion of program.