I finally decided to send some of my art to Dark Horse, DC and Marvel.
So, I stopped by their recpectives websites to get the submissions instructions and, what a surprise, DC and Marvel only accept submissions at Comic book conventions; not even via Mail. Sadly, there are no one of these three attending to Montreal Comic Con.
Anyway, I sent a package to DH and, well, wait to see if I'll get, at least, an answer...
Is there any other editors, with decent page rate and payment process, where I can send art sample?