planning on travel with my partner to see friends in montreal

[canadamydream]

my partner and I we would like to go to visit friends in canada. we have not aply for visiting visa yet. but i have a friend who when to canadian embassy in mexico to get his visa and it was rejected. eventhough he shows all the paper work need it for the visa. also i been searching and find that there are many agencies in mexico who help with the visa procedures. my question is which way is better to get a canadian visa by some agency or aplying ourselfs at the canadian embassy? thanx for all your responses.